diff --git a/electron/index.html b/electron/index.html
index f20118b..483de86 100644
--- a/electron/index.html
+++ b/electron/index.html
@@ -18,7 +18,11 @@
                 </div>
             </div>
             <nav class="category-nav">
-                <div class="category-item active" data-category="libplugin" title="libplugin">
+                <div class="category-item" data-category="home" title="Home">
+                    <div class="category-icon" style="background-color: #6366f1;">🏠</div>
+                    <span class="category-label">Home</span>
+                </div>
+                <div class="category-item" data-category="libplugin" title="libplugin">
                     <div class="category-icon" style="background-color: #3b82f6;">LP</div>
                     <span class="category-label">libplugin</span>
                 </div>
@@ -67,14 +71,15 @@
                 </div>
             </div>
 
-            <!-- OPAT Core content (empty for now) -->
+            <!-- OPAT Core content -->
             <div class="sidebar-content hidden" data-category="opat">
                 <div class="sidebar-header">
                     <h3>OPAT Core</h3>
                 </div>
-                <div class="empty-state">
-                    <p>OPAT tools coming soon...</p>
-                </div>
+                <nav class="sidebar-nav">
+                    <input type="file" id="opat-file-input" accept=".opat" class="opat-file-input" style="display: none;"/>
+                    <button id="opat-browse-btn" class="nav-button active">Open OPAT File</button>
+                </nav>
             </div>
 
             <!-- SERiF Libraries content (empty for now) -->
@@ -89,9 +94,254 @@
         </aside>
 
         <main class="content-area">
-            <div id="welcome-screen">
-                <h1>Welcome to 4DSTAR Bundle Manager</h1>
-                <p>Open or create a bundle to get started.</p>
+            <!-- Main Home Screen -->
+            <div id="welcome-screen" class="home-screen">
+                <div class="welcome-hero">
+                    <div class="welcome-logo">
+                        <div class="star-icon-large">✦</div>
+                        <h1 class="welcome-title">4DSTAR</h1>
+                        <p class="welcome-subtitle">Stellar Evolution Analysis Suite</p>
+                    </div>
+                </div>
+                
+                <div class="welcome-content">
+                    <div class="welcome-section">
+                        <h2>Getting Started</h2>
+                        <p>Choose a tool from the sidebar to begin your analysis:</p>
+                        
+                        <div class="feature-grid">
+                            <div class="feature-card">
+                                <div class="feature-icon" style="background-color: #3b82f6;">LP</div>
+                                <div class="feature-info">
+                                    <h3>libplugin Bundle Manager</h3>
+                                    <p>Create, open, and manage stellar evolution bundles. Build models and analyze results.</p>
+                                </div>
+                            </div>
+                            
+                            <div class="feature-card">
+                                <div class="feature-icon" style="background-color: #f59e0b;">OC</div>
+                                <div class="feature-info">
+                                    <h3>OPAT File Inspector</h3>
+                                    <p>Inspect and analyze OPAT (Opacity Table) files. View table data and explore index vectors.</p>
+                                </div>
+                            </div>
+                            
+                            <div class="feature-card">
+                                <div class="feature-icon" style="background-color: #10b981;">LC</div>
+                                <div class="feature-info">
+                                    <h3>libconstants</h3>
+                                    <p>Access and manage physical constants and parameters for stellar evolution calculations.</p>
+                                </div>
+                            </div>
+                            
+                            <div class="feature-card">
+                                <div class="feature-icon" style="background-color: #ef4444;">SL</div>
+                                <div class="feature-info">
+                                    <h3>SERiF Libraries</h3>
+                                    <p>Stellar Evolution Rapid interpolation Framework tools and utilities.</p>
+                                </div>
+                            </div>
+                        </div>
+                    </div>
+                    
+                    <div class="welcome-tips">
+                        <h3>Quick Tips</h3>
+                        <ul>
+                            <li>Use the sidebar navigation to switch between different tools</li>
+                            <li>Each tool has its own dedicated workspace and features</li>
+                            <li>File operations and settings are accessible from the top menu bar</li>
+                            <li>Hover over sidebar icons for quick tool descriptions</li>
+                        </ul>
+                    </div>
+                </div>
+            </div>
+
+            <!-- libplugin Home Screen -->
+            <div id="libplugin-home" class="home-screen hidden">
+                <div class="category-hero">
+                    <div class="category-hero-content">
+                        <div class="category-icon-large" style="background-color: #3b82f6;">LP</div>
+                        <h1 class="category-title">libplugin Bundle Manager</h1>
+                        <p class="category-subtitle">Create, manage, and analyze stellar evolution bundles</p>
+                    </div>
+                </div>
+                
+                <div class="category-content">
+                    <div class="feature-section">
+                        <h2>Bundle Management</h2>
+                        <div class="action-cards">
+                            <div class="action-card">
+                                <h3>📁 Open Bundle</h3>
+                                <p>Load an existing stellar evolution bundle for analysis and modification.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>➕ Create Bundle</h3>
+                                <p>Start a new stellar evolution project with custom parameters and configurations.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>🔧 Build Models</h3>
+                                <p>Compile and execute stellar evolution calculations with your bundle settings.</p>
+                            </div>
+                        </div>
+                    </div>
+                    
+                    <div class="info-section">
+                        <h3>About libplugin</h3>
+                        <p>The libplugin Bundle Manager provides a comprehensive interface for managing stellar evolution projects. Create bundles with specific initial conditions, track evolution parameters, and analyze results through integrated tools.</p>
+                    </div>
+                </div>
+            </div>
+
+            <!-- OPAT Home Screen -->
+            <div id="opat-home" class="home-screen hidden">
+                <div class="category-hero">
+                    <div class="category-hero-content">
+                        <div class="category-icon-large" style="background-color: #f59e0b;">OC</div>
+                        <h1 class="category-title">OPAT File Inspector</h1>
+                        <p class="category-subtitle">Analyze opacity tables and stellar atmosphere data</p>
+                    </div>
+                </div>
+                
+                <div class="category-content">
+                    <div class="feature-section">
+                        <h2>OPAT Analysis Tools</h2>
+                        <div class="action-cards">
+                            <div class="action-card">
+                                <h3>📊 Load OPAT File</h3>
+                                <p>Import and parse OPAT (Opacity Table) files for detailed inspection.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>🔍 Explore Data</h3>
+                                <p>Navigate through index vectors and examine table structures and metadata.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>📈 View Tables</h3>
+                                <p>Display opacity data in interactive tables with full or filtered views.</p>
+                            </div>
+                        </div>
+                    </div>
+                    
+                    <div class="info-section">
+                        <h3>About OPAT Files</h3>
+                        <p>OPAT (Opacity Table) files contain crucial stellar atmosphere data including opacity coefficients, temperature and density grids, and related thermodynamic properties used in stellar evolution calculations.</p>
+                    </div>
+                </div>
+            </div>
+
+            <!-- libconstants Home Screen -->
+            <div id="libconstants-home" class="home-screen hidden">
+                <div class="category-hero">
+                    <div class="category-hero-content">
+                        <div class="category-icon-large" style="background-color: #10b981;">LC</div>
+                        <h1 class="category-title">libconstants</h1>
+                        <p class="category-subtitle">Physical constants and stellar parameters</p>
+                    </div>
+                </div>
+                
+                <div class="category-content">
+                    <div class="feature-section">
+                        <h2>Constants Management</h2>
+                        <div class="action-cards">
+                            <div class="action-card">
+                                <h3>🔢 Physical Constants</h3>
+                                <p>Access fundamental physical constants used in stellar evolution calculations.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>⭐ Stellar Parameters</h3>
+                                <p>Manage stellar-specific constants and conversion factors.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>⚙️ Configuration</h3>
+                                <p>Customize constant values and units for specific research needs.</p>
+                            </div>
+                        </div>
+                    </div>
+                    
+                    <div class="info-section">
+                        <h3>About libconstants</h3>
+                        <p>The libconstants module provides a centralized repository of physical constants, conversion factors, and stellar parameters essential for accurate stellar evolution modeling and analysis.</p>
+                    </div>
+                </div>
+            </div>
+
+            <!-- SERiF Home Screen -->
+            <div id="serif-home" class="home-screen hidden">
+                <div class="category-hero">
+                    <div class="category-hero-content">
+                        <div class="category-icon-large" style="background-color: #ef4444;">SL</div>
+                        <h1 class="category-title">SERiF Libraries</h1>
+                        <p class="category-subtitle">Stellar Evolution Rapid interpolation Framework</p>
+                    </div>
+                </div>
+                
+                <div class="category-content">
+                    <div class="feature-section">
+                        <h2>SERiF Tools</h2>
+                        <div class="action-cards">
+                            <div class="action-card">
+                                <h3>🚀 Rapid Interpolation</h3>
+                                <p>High-performance interpolation algorithms for stellar evolution tracks.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>📚 Model Libraries</h3>
+                                <p>Access pre-computed stellar evolution models and isochrones.</p>
+                            </div>
+                            <div class="action-card">
+                                <h3>🔬 Analysis Framework</h3>
+                                <p>Advanced tools for stellar population synthesis and comparison studies.</p>
+                            </div>
+                        </div>
+                    </div>
+                    
+                    <div class="info-section">
+                        <h3>About SERiF</h3>
+                        <p>The Stellar Evolution Rapid interpolation Framework (SERiF) provides optimized tools for working with large stellar evolution datasets, enabling fast interpolation and analysis of stellar models.</p>
+                    </div>
+                </div>
+            </div>
+
+            <div id="opat-view" class="hidden">
+                <header class="content-header">
+                    <h2 id="opat-title">OPAT File Inspector</h2>
+                    <div class="action-buttons">
+                        <button id="opat-close-btn">Close File</button>
+                    </div>
+                </header>
+
+                <div class="tab-nav">
+                    <button class="tab-link active" data-tab="opat-overview-tab">File Information</button>
+                    <button class="tab-link" data-tab="opat-explorer-tab">Data Explorer</button>
+                </div>
+
+                <div id="opat-tab-content">
+                    <div id="opat-overview-tab" class="tab-pane active">
+                        <div id="opat-header-info" class="opat-info-content"></div>
+                        <div class="opat-info-section">
+                            <h4 class="opat-section-title">All Table Tags</h4>
+                            <ul id="opat-all-tags-list" class="opat-tags-list"></ul>
+                        </div>
+                    </div>
+
+                    <div id="opat-explorer-tab" class="tab-pane hidden">
+                        <div class="opat-info-section">
+                            <h4 class="opat-section-title">Data Card Explorer</h4>
+                            <div class="opat-selector-group">
+                                <label for="opat-index-selector" class="opat-label">Select Index Vector:</label>
+                                <select id="opat-index-selector" class="opat-select">
+                                    <option value="">-- Select an Index Vector --</option>
+                                </select>
+                            </div>
+                            <div id="opat-tables-display" class="opat-tables-display"></div>
+                        </div>
+
+                        <div class="opat-info-section">
+                            <h4 class="opat-section-title">Table Viewer</h4>
+                            <div id="opat-table-data-content" class="opat-table-viewer">
+                                <p class="opat-placeholder">Click on a table from the 'Data Card Explorer' above to view its data here.</p>
+                            </div>
+                        </div>
+                    </div>
+                </div>
             </div>
 
             <div id="bundle-view" class="hidden">
@@ -309,6 +559,7 @@
 
     <div id="spinner" class="spinner hidden"></div>
 
+    <script src="opatParser.js"></script>
     <script src="renderer.js"></script>
 </body>
 
diff --git a/electron/opatParser.js b/electron/opatParser.js
new file mode 100644
index 0000000..799e105
--- /dev/null
+++ b/electron/opatParser.js
@@ -0,0 +1,375 @@
+/**
+ * A helper class to read binary data from an ArrayBuffer.
+ * It keeps track of the current position and handles reading different data types.
+ */
+class DataReader {
+    /**
+     * @param {ArrayBuffer} arrayBuffer The file content.
+     */
+    constructor(arrayBuffer) {
+        this.dataView = new DataView(arrayBuffer);
+        this.decoder = new TextDecoder();
+        this.offset = 0;
+    }
+
+    seek(newOffset) {
+        this.offset = newOffset;
+    }
+
+    readString(length) {
+        const strBytes = new Uint8Array(this.dataView.buffer, this.offset, length);
+        this.offset += length;
+        // Trim null characters from the end
+        const firstNull = strBytes.indexOf(0);
+        const nonNullSlice = firstNull === -1 ? strBytes : strBytes.slice(0, firstNull);
+        return this.decoder.decode(nonNullSlice);
+    }
+
+    readBytes(length) {
+        const bytes = new Uint8Array(this.dataView.buffer, this.offset, length);
+        this.offset += length;
+        return bytes;
+    }
+
+    readUint8() {
+        const value = this.dataView.getUint8(this.offset, true);
+        this.offset += 1;
+        return value;
+    }
+
+    readUint16() {
+        const value = this.dataView.getUint16(this.offset, true);
+        this.offset += 2;
+        return value;
+    }
+
+    readUint32() {
+        const value = this.dataView.getUint32(this.offset, true);
+        this.offset += 4;
+        return value;
+    }
+
+    readUint64() {
+        const value = this.dataView.getBigUint64(this.offset, true);
+        this.offset += 8;
+        return value;
+    }
+
+    readFloat64() {
+        const value = this.dataView.getFloat64(this.offset, true);
+        this.offset += 8;
+        return value;
+    }
+
+    readFloat64Array(length) {
+        const byteLength = length * 8;
+        const values = new Float64Array(this.dataView.buffer, this.offset, length);
+        this.offset += byteLength;
+        return values;
+    }
+}
+
+/**
+ * Corresponds to the Header struct in opatIO.h
+ */
+class Header {
+    constructor() {
+        this.magic = "";
+        this.version = 0;
+        this.numTables = 0;
+        this.headerSize = 0;
+        this.indexOffset = 0n; // BigInt
+        this.creationDate = "";
+        this.sourceInfo = "";
+        this.comment = "";
+        this.numIndex = 0;
+        this.hashPrecision = 0;
+        this.reserved = null;
+    }
+
+    static fromReader(reader) {
+        const h = new Header();
+        h.magic = reader.readString(4);
+        h.version = reader.readUint16();
+        h.numTables = reader.readUint32();
+        h.headerSize = reader.readUint32();
+        h.indexOffset = reader.readUint64();
+        h.creationDate = reader.readString(16);
+        h.sourceInfo = reader.readString(64);
+        h.comment = reader.readString(128);
+        h.numIndex = reader.readUint16();
+        h.hashPrecision = reader.readUint8();
+        h.reserved = reader.readBytes(23);
+        return h;
+    }
+}
+
+
+/**
+ * Corresponds to the CardHeader struct in opatIO.h
+ */
+class CardHeader {
+    constructor() {
+        this.magic = "";
+        this.numTables = 0;
+        this.headerSize = 0;
+        this.indexOffset = 0n;
+        this.cardSize = 0n;
+        this.comment = "";
+        this.reserved = null;
+    }
+
+    static fromReader(reader) {
+        const h = new CardHeader();
+        h.magic = reader.readString(4);
+        h.numTables = reader.readUint32();
+        h.headerSize = reader.readUint32();
+        h.indexOffset = reader.readUint64();
+        h.cardSize = reader.readUint64();
+        h.comment = reader.readString(128);
+        h.reserved = reader.readBytes(100);
+        return h;
+    }
+}
+
+
+/**
+ * Corresponds to the CardCatalogEntry struct in opatIO.h
+ */
+class CardCatalogEntry {
+    constructor() {
+        this.index = []; // This will be an array of numbers (FloatIndexVector)
+        this.byteStart = 0n;
+        this.byteEnd = 0n;
+        this.sha256 = null; // Uint8Array
+    }
+
+    /**
+     * In JS, we can use a stringified version of the index vector as a key for Maps.
+     */
+    getKey() {
+        return JSON.stringify(this.index);
+    }
+
+    static fromReader(reader, numIndex) {
+        const entry = new CardCatalogEntry();
+        entry.index = Array.from(reader.readFloat64Array(numIndex));
+        entry.byteStart = reader.readUint64();
+        entry.byteEnd = reader.readUint64();
+        entry.sha256 = reader.readBytes(32);
+        return entry;
+    }
+}
+
+
+/**
+ * Corresponds to the TableIndexEntry struct in opatIO.h
+ */
+class TableIndexEntry {
+    constructor() {
+        this.tag = "";
+        this.byteStart = 0n;
+        this.byteEnd = 0n;
+        this.numColumns = 0;
+        this.numRows = 0;
+        this.columnName = "";
+        this.rowName = "";
+        this.size = 0n; // Vector size of each cell
+        this.reserved = null;
+    }
+
+    static fromReader(reader) {
+        const entry = new TableIndexEntry();
+        entry.tag = reader.readString(8);
+        entry.byteStart = reader.readUint64();
+        entry.byteEnd = reader.readUint64();
+        entry.numColumns = reader.readUint16();
+        entry.numRows = reader.readUint16();
+        entry.columnName = reader.readString(8);
+        entry.rowName = reader.readString(8);
+        entry.size = reader.readUint64();
+        entry.reserved = reader.readBytes(12);
+        return entry;
+    }
+}
+
+
+/**
+ * Corresponds to the OPATTable struct in opatIO.h
+ */
+class OPATTable {
+    constructor() {
+        this.rowValues = new Float64Array(0);
+        this.columnValues = new Float64Array(0);
+        this.data = new Float64Array(0);
+        this.N_R = 0;
+        this.N_C = 0;
+        this.m_vsize = 0;
+    }
+
+    /**
+     * Gets the vector at a specific cell.
+     * @param {number} row The row index.
+     * @param {number} column The column index.
+     * @returns {Float64Array} The vector data in the cell.
+     */
+    getData(row, column) {
+        if (row >= this.N_R || column >= this.N_C) {
+            throw new Error("Index out of range");
+        }
+        const startIndex = (row * this.N_C + column) * this.m_vsize;
+        return this.data.subarray(startIndex, startIndex + this.m_vsize);
+    }
+
+    /**
+     * Gets a single primitive value from a cell.
+     * @param {number} row
+     * @param {number} column
+     * @param {number} zdepth The index within the cell's vector.
+     */
+    getValue(row, column, zdepth = 0) {
+        if (row >= this.N_R || column >= this.N_C || zdepth >= this.m_vsize) {
+            throw new Error("Index out of range");
+        }
+        const index = (row * this.N_C + column) * this.m_vsize + zdepth;
+        return this.data[index];
+    }
+
+    static fromReader(reader, cardEntry, tableEntry) {
+        const table = new OPATTable();
+        table.N_R = tableEntry.numRows;
+        table.N_C = tableEntry.numColumns;
+        table.m_vsize = Number(tableEntry.size); // Convert BigInt to Number
+
+        reader.seek(Number(cardEntry.byteStart) + Number(tableEntry.byteStart));
+
+        table.rowValues = reader.readFloat64Array(table.N_R);
+        table.columnValues = reader.readFloat64Array(table.N_C);
+
+        const dataSize = table.N_R * table.N_C * table.m_vsize;
+        table.data = reader.readFloat64Array(dataSize);
+
+        return table;
+    }
+}
+
+/**
+ * Corresponds to the DataCard struct in opatIO.h
+ */
+class DataCard {
+    constructor() {
+        /** @type {CardHeader} */
+        this.header = null;
+        /** @type {Map<string, TableIndexEntry>} */
+        this.tableIndex = new Map();
+        /** @type {Map<string, OPATTable>} */
+        this.tableData = new Map();
+    }
+
+    /**
+     * Get a table by its tag name.
+     * @param {string} tag The tag of the table to retrieve.
+     * @returns {OPATTable | undefined}
+     */
+    get(tag) {
+        return this.tableData.get(tag);
+    }
+
+    static fromReader(reader, cardCatalogEntry) {
+        const card = new DataCard();
+        reader.seek(Number(cardCatalogEntry.byteStart));
+
+        // 1. Read Card Header
+        card.header = CardHeader.fromReader(reader);
+
+        // 2. Read Table Index
+        reader.seek(Number(cardCatalogEntry.byteStart) + Number(card.header.indexOffset));
+        for (let i = 0; i < card.header.numTables; i++) {
+            const tableIndexEntry = TableIndexEntry.fromReader(reader);
+            card.tableIndex.set(tableIndexEntry.tag, tableIndexEntry);
+        }
+
+        // 3. Read all Table Data within this card
+        for (const [tag, tableEntry] of card.tableIndex.entries()) {
+            const table = OPATTable.fromReader(reader, cardCatalogEntry, tableEntry);
+            card.tableData.set(tag, table);
+        }
+
+        return card;
+    }
+}
+
+
+/**
+ * The main class representing an entire OPAT file.
+ */
+class OPAT {
+    constructor() {
+        /** @type {Header} */
+        this.header = null;
+        /** @type {Map<string, CardCatalogEntry>} */
+        this.cardCatalog = new Map();
+        /** @type {Map<string, DataCard>} */
+        this.cards = new Map();
+    }
+
+    /**
+     * Get a DataCard by its index vector.
+     * @param {number[]} index The index vector (e.g., [1.0, 2.5]).
+     * @returns {DataCard | undefined}
+     */
+    get(index) {
+        const key = JSON.stringify(index);
+        return this.cards.get(key);
+    }
+
+    /**
+     * Calculates and returns the bounds for each dimension.
+     * @returns {Array<{min: number, max: number}>}
+     */
+    getBounds() {
+        const bounds = Array(this.header.numIndex).fill(null).map(() => ({
+            min: Infinity,
+            max: -Infinity
+        }));
+
+        for (const entry of this.cardCatalog.values()) {
+            for (let i = 0; i < this.header.numIndex; i++) {
+                bounds[i].min = Math.min(bounds[i].min, entry.index[i]);
+                bounds[i].max = Math.max(bounds[i].max, entry.index[i]);
+            }
+        }
+        return bounds;
+    }
+}
+
+/**
+ * Main parsing function. Reads an ArrayBuffer and returns an OPAT object.
+ * @param {ArrayBuffer} arrayBuffer The content of the .opat file.
+ * @returns {OPAT} The parsed OPAT object.
+ */
+function parseOPAT(arrayBuffer) {
+    const reader = new DataReader(arrayBuffer);
+    const opat = new OPAT();
+
+    // 1. Read Header
+    opat.header = Header.fromReader(reader);
+    if (opat.header.magic !== "OPAT") {
+        throw new Error("File is not a valid OPAT file.");
+    }
+
+    // 2. Read Card Catalog
+    reader.seek(Number(opat.header.indexOffset)); // Seek to where the catalog starts
+    for (let i = 0; i < opat.header.numTables; i++) {
+        const entry = CardCatalogEntry.fromReader(reader, opat.header.numIndex);
+        opat.cardCatalog.set(entry.getKey(), entry);
+    }
+
+    // 3. Read all DataCards
+    for (const entry of opat.cardCatalog.values()) {
+        const dataCard = DataCard.fromReader(reader, entry);
+        opat.cards.set(entry.getKey(), dataCard);
+    }
+
+    return opat;
+}
\ No newline at end of file
diff --git a/electron/renderer.js b/electron/renderer.js
index f7db468..e9f69b3 100644
--- a/electron/renderer.js
+++ b/electron/renderer.js
@@ -51,6 +51,26 @@ document.addEventListener('DOMContentLoaded', async () => {
   // Initialize DOM elements
   initializeDOMElements();
   
+  // Initialize OPAT tab navigation
+  initializeOPATTabs();
+
+  // Initialize OPAT UI elements
+  initializeOPATElements();
+
+  // Initialize home screen - set home as default active category
+  const homeCategory = document.querySelector('.category-item[data-category="home"]');
+  const secondarySidebar = document.getElementById('secondary-sidebar');
+  
+  if (homeCategory) {
+    homeCategory.classList.add('active');
+    showCategoryHomeScreen('home');
+    
+    // Hide secondary sidebar on initial load since we start with home
+    if (secondarySidebar) {
+      secondarySidebar.style.display = 'none';
+    }
+  }
+  
   // Set initial view
   showView('welcome-screen');
 
@@ -221,6 +241,8 @@ function setupEventListeners() {
     fillTargetsContent.classList.add('hidden');
   }
 
+
+
   // Check if bundle is signed and show warning before bundle-modifying operations
   function checkSignatureAndWarn(operation, operationName = 'operation') {
     const isSigned = currentBundle && 
@@ -287,6 +309,7 @@ function setupEventListeners() {
   categoryItems.forEach(categoryItem => {
     categoryItem.addEventListener('click', () => {
       const selectedCategory = categoryItem.getAttribute('data-category');
+      const secondarySidebar = document.getElementById('secondary-sidebar');
       
       // Remove active class from all category items
       categoryItems.forEach(item => item.classList.remove('active'));
@@ -297,17 +320,30 @@ function setupEventListeners() {
       // Hide all sidebar contents
       sidebarContents.forEach(content => content.classList.add('hidden'));
       
-      // Show selected category content
-      const selectedContent = document.querySelector(`.sidebar-content[data-category="${selectedCategory}"]`);
-      if (selectedContent) {
-        selectedContent.classList.remove('hidden');
+      // Show/hide secondary sidebar based on category
+      if (selectedCategory === 'home') {
+        // Hide the entire secondary sidebar on home screen
+        if (secondarySidebar) {
+          secondarySidebar.style.display = 'none';
+        }
+      } else {
+        // Show secondary sidebar and its content for other categories
+        if (secondarySidebar) {
+          secondarySidebar.style.display = 'flex';
+        }
+        const selectedContent = document.querySelector(`.sidebar-content[data-category="${selectedCategory}"]`);
+        if (selectedContent) {
+          selectedContent.classList.remove('hidden');
+        }
       }
       
-      // Update welcome screen title based on selected category
-      updateWelcomeScreen(selectedCategory);
+      // Show appropriate home screen
+      showCategoryHomeScreen(selectedCategory);
     });
   });
 
+
+
   // Update welcome screen based on selected category
   function updateWelcomeScreen(category) {
     const welcomeTitle = document.querySelector('#welcome-screen h1');
@@ -995,3 +1031,360 @@ async function reloadCurrentBundle() {
     displayBundleInfo(result.report);
   }
 }
+
+// ===== OPAT FILE INSPECTOR LOGIC =====
+// OPAT File Inspector variables
+let currentOPATFile = null;
+let opatFileInput, opatBrowseBtn, opatView, opatCloseBtn;
+let opatHeaderInfo, opatAllTagsList, opatIndexSelector, opatTablesDisplay, opatTableDataContent;
+
+// Helper function to hide all views
+function hideAllViews() {
+  const welcomeScreen = document.getElementById('welcome-screen');
+  const libpluginHome = document.getElementById('libplugin-home');
+  const opatHome = document.getElementById('opat-home');
+  const libconstantsHome = document.getElementById('libconstants-home');
+  const serifHome = document.getElementById('serif-home');
+  const opatView = document.getElementById('opat-view');
+  const libpluginView = document.getElementById('libplugin-view');
+
+  if (welcomeScreen) welcomeScreen.classList.add('hidden');
+  if (libpluginHome) libpluginHome.classList.add('hidden');
+  if (opatHome) opatHome.classList.add('hidden');
+  if (libconstantsHome) libconstantsHome.classList.add('hidden');
+  if (serifHome) serifHome.classList.add('hidden');
+  if (opatView) opatView.classList.add('hidden');
+  if (libpluginView) libpluginView.classList.add('hidden');
+}
+
+// Show appropriate home screen based on selected category
+function showCategoryHomeScreen(category) {
+  hideAllViews();
+  
+  switch (category) {
+    case 'home':
+      const welcomeScreen = document.getElementById('welcome-screen');
+      if (welcomeScreen) welcomeScreen.classList.remove('hidden');
+      break;
+    case 'libplugin':
+      const libpluginHome = document.getElementById('libplugin-home');
+      if (libpluginHome) libpluginHome.classList.remove('hidden');
+      break;
+    case 'opat':
+      const opatHome = document.getElementById('opat-home');
+      if (opatHome) opatHome.classList.remove('hidden');
+      break;
+    case 'libconstants':
+      const libconstantsHome = document.getElementById('libconstants-home');
+      if (libconstantsHome) libconstantsHome.classList.remove('hidden');
+      break;
+    case 'serif':
+      const serifHome = document.getElementById('serif-home');
+      if (serifHome) serifHome.classList.remove('hidden');
+      break;
+    default:
+      const defaultWelcome = document.getElementById('welcome-screen');
+      if (defaultWelcome) defaultWelcome.classList.remove('hidden');
+  }
+}
+
+// Initialize OPAT UI elements in DOMContentLoaded
+function initializeOPATElements() {
+    opatFileInput = document.getElementById('opat-file-input');
+    opatBrowseBtn = document.getElementById('opat-browse-btn');
+    opatView = document.getElementById('opat-view');
+    opatCloseBtn = document.getElementById('opat-close-btn');
+    opatHeaderInfo = document.getElementById('opat-header-info');
+    opatAllTagsList = document.getElementById('opat-all-tags-list');
+    opatIndexSelector = document.getElementById('opat-index-selector');
+    opatTablesDisplay = document.getElementById('opat-tables-display');
+    opatTableDataContent = document.getElementById('opat-table-data-content');
+
+    // Event listeners
+    opatBrowseBtn.addEventListener('click', () => opatFileInput.click());
+    opatFileInput.addEventListener('change', handleOPATFileSelection);
+    opatIndexSelector.addEventListener('change', handleIndexVectorChange);
+    opatCloseBtn.addEventListener('click', closeOPATFile);
+
+    // Initialize OPAT tab navigation
+    initializeOPATTabs();
+    
+    // Add window resize listener to update table heights
+    window.updateTableHeights = function() {
+        const newHeight = Math.max(300, window.innerHeight - 450);
+        
+        // Target the main table containers
+        const containers = document.querySelectorAll('.opat-table-container');
+        containers.forEach((container, index) => {
+            container.style.setProperty('height', newHeight + 'px', 'important');
+        });
+        
+        // Also target the scroll wrappers
+        const scrollWrappers = document.querySelectorAll('.table-scroll-wrapper');
+        scrollWrappers.forEach((wrapper, index) => {
+            wrapper.style.setProperty('height', '100%', 'important');
+        });
+    };
+    
+    window.addEventListener('resize', () => {
+        console.log('Window resize event fired');
+        window.updateTableHeights();
+    });
+    
+    // Also update on initial load and when tables are displayed
+    setTimeout(window.updateTableHeights, 100);
+}
+
+function closeOPATFile() {
+    currentOPATFile = null;
+    opatFileInput.value = '';
+    resetOPATViewerState();
+    hideAllViews();
+    document.getElementById('welcome-screen').classList.remove('hidden');
+}
+
+function resetOPATViewerState() {
+    // Clear all OPAT content areas
+    if (opatHeaderInfo) opatHeaderInfo.innerHTML = '';
+    if (opatAllTagsList) opatAllTagsList.innerHTML = '';
+    if (opatIndexSelector) {
+        opatIndexSelector.innerHTML = '<option value="">-- Select an Index Vector --</option>';
+    }
+    if (opatTablesDisplay) opatTablesDisplay.innerHTML = '';
+    if (opatTableDataContent) {
+        opatTableDataContent.innerHTML = '<p class="opat-placeholder">Click on a table from the \'Data Card Explorer\' above to view its data here.</p>';
+    }
+    
+    // Reset to File Information tab
+    const opatTabLinks = document.querySelectorAll('#opat-view .tab-link');
+    const opatTabPanes = document.querySelectorAll('#opat-tab-content .tab-pane');
+    
+    opatTabLinks.forEach(link => link.classList.remove('active'));
+    opatTabPanes.forEach(pane => pane.classList.add('hidden'));
+    
+    // Activate File Information tab
+    const fileInfoTab = document.querySelector('[data-tab="opat-overview-tab"]');
+    const fileInfoPane = document.getElementById('opat-overview-tab');
+    if (fileInfoTab) fileInfoTab.classList.add('active');
+    if (fileInfoPane) fileInfoPane.classList.remove('hidden');
+}
+
+function initializeOPATTabs() {
+    const opatTabLinks = document.querySelectorAll('#opat-view .tab-link');
+    const opatTabPanes = document.querySelectorAll('#opat-tab-content .tab-pane');
+    
+    opatTabLinks.forEach(link => {
+        link.addEventListener('click', (e) => {
+            e.preventDefault();
+            const targetTab = link.getAttribute('data-tab');
+            
+            // Remove active class from all tabs and panes
+            opatTabLinks.forEach(l => l.classList.remove('active'));
+            opatTabPanes.forEach(p => p.classList.add('hidden'));
+            
+            // Add active class to clicked tab and show corresponding pane
+            link.classList.add('active');
+            document.getElementById(targetTab).classList.remove('hidden');
+        });
+    });
+}
+
+
+
+async function handleOPATFileSelection(event) {
+    const file = event.target.files[0];
+    if (!file) return;
+
+    try {
+        // Reset viewer state before loading new file
+        resetOPATViewerState();
+        
+        const arrayBuffer = await file.arrayBuffer();
+        currentOPATFile = parseOPAT(arrayBuffer);
+        
+        displayOPATFileInfo();
+        populateIndexSelector();
+        
+        // Show OPAT view and hide other views
+        hideAllViews();
+        opatView.classList.remove('hidden');
+        
+        // Update title with filename
+        document.getElementById('opat-title').textContent = `OPAT File Inspector - ${file.name}`;
+        
+    } catch (error) {
+        console.error('Error parsing OPAT file:', error);
+        showModal('Error', `Failed to parse OPAT file: ${error.message}`);
+    }
+}
+
+function displayOPATFileInfo() {
+    if (!currentOPATFile) return;
+    
+    const header = currentOPATFile.header;
+    opatHeaderInfo.innerHTML = `
+        <div class="opat-info-section">
+            <h4 class="opat-section-title">Header Information</h4>
+            <div class="info-grid">
+                <p><strong>Magic:</strong> ${header.magic}</p>
+                <p><strong>Version:</strong> ${header.version}</p>
+                <p><strong>Number of Tables:</strong> ${header.numTables}</p>
+                <p><strong>Header Size:</strong> ${header.headerSize} bytes</p>
+                <p><strong>Index Offset:</strong> ${header.indexOffset}</p>
+                <p><strong>Creation Date:</strong> ${header.creationDate}</p>
+                <p><strong>Source Info:</strong> ${header.sourceInfo}</p>
+                <p><strong>Comment:</strong> ${header.comment || 'None'}</p>
+                <p><strong>Number of Indices:</strong> ${header.numIndex}</p>
+                <p><strong>Hash Precision:</strong> ${header.hashPrecision}</p>
+            </div>
+        </div>
+    `;
+    
+    // Display all unique table tags
+    displayAllTableTags();
+}
+
+function displayAllTableTags() {
+    if (!currentOPATFile) return;
+    
+    const allTags = new Set();
+    for (const card of currentOPATFile.cards.values()) {
+        for (const tag of card.tableIndex.keys()) {
+            allTags.add(tag);
+        }
+    }
+    
+    opatAllTagsList.innerHTML = '';
+    Array.from(allTags).sort().forEach(tag => {
+        const li = document.createElement('li');
+        li.textContent = tag;
+        opatAllTagsList.appendChild(li);
+    });
+}
+
+function populateIndexSelector() {
+    if (!currentOPATFile) return;
+    
+    opatIndexSelector.innerHTML = '<option value="">-- Select an index vector --</option>';
+    
+    for (const [key, entry] of currentOPATFile.cardCatalog.entries()) {
+        const option = document.createElement('option');
+        option.value = key;
+        option.textContent = `[${entry.index.join(', ')}]`;
+        opatIndexSelector.appendChild(option);
+    }
+}
+
+function handleIndexVectorChange() {
+    const selectedKey = opatIndexSelector.value;
+    if (!selectedKey || !currentOPATFile) {
+        opatTablesDisplay.innerHTML = '';
+        return;
+    }
+    
+    const card = currentOPATFile.cards.get(selectedKey);
+    if (!card) return;
+    
+    opatTablesDisplay.innerHTML = '';
+    
+    for (const [tag, tableEntry] of card.tableIndex.entries()) {
+        const tableInfo = document.createElement('div');
+        tableInfo.className = 'opat-table-info';
+        tableInfo.innerHTML = `
+            <div class="opat-table-tag">${tag}</div>
+            <div class="opat-table-details">
+                Rows: ${tableEntry.numRows}, Columns: ${tableEntry.numColumns}<br>
+                Row Name: ${tableEntry.rowName}, Column Name: ${tableEntry.columnName}
+            </div>
+        `;
+        
+        tableInfo.addEventListener('click', () => {
+            const table = card.tableData.get(tag);
+            displayTableData(table, tag);
+        });
+        
+        opatTablesDisplay.appendChild(tableInfo);
+    }
+}
+
+function displayTableData(table, tag, showAll = false) {
+    if (!table) {
+        opatTableDataContent.innerHTML = '<p class="opat-placeholder">Table not found.</p>';
+        return;
+    }
+
+    let html = `<div class="opat-table-title"><span class="opat-table-tag-highlight">${tag}</span> Table Data</div>`;
+    html += `<p><strong>Dimensions:</strong> ${table.N_R} rows × ${table.N_C} columns × ${table.m_vsize} values per cell</p>`;
+    
+    if (table.N_R > 0 && table.N_C > 0) {
+        if (table.m_vsize === 0 || table.data.length === 0) {
+            html += '<p><strong>Note:</strong> This table has no data values (m_vsize = 0 or empty data array).</p>';
+            html += '<p>The table structure exists but contains no numerical data to display.</p>';
+        } else {
+            // Add show all/show less toggle buttons
+            if (table.N_R > 50) {
+                html += '<div class="table-controls">';
+                if (!showAll) {
+                    html += `<button class="show-all-btn" onclick="displayTableData(currentOPATFile.cards.get('${opatIndexSelector.value}').tableData.get('${tag}'), '${tag}', true)">Show All ${table.N_R} Rows</button>`;
+                } else {
+                    html += `<button class="show-less-btn" onclick="displayTableData(currentOPATFile.cards.get('${opatIndexSelector.value}').tableData.get('${tag}'), '${tag}', false)">Show First 50 Rows</button>`;
+                }
+                html += '</div>';
+            }
+            
+            html += '<div class="opat-table-container">';
+            html += '<div class="table-scroll-wrapper">';
+            html += '<table class="opat-data-table">';
+            
+            // Header row
+            html += '<thead><tr><th class="corner-cell"></th>';
+            for (let c = 0; c < table.N_C; c++) {
+                html += `<th>${table.columnValues[c].toFixed(3)}</th>`;
+            }
+            html += '</tr></thead>';
+            
+            // Data rows
+            html += '<tbody>';
+            const rowsToShow = showAll ? table.N_R : Math.min(table.N_R, 50);
+            for (let r = 0; r < rowsToShow; r++) {
+                html += '<tr>';
+                html += `<th class="row-header">${table.rowValues[r].toFixed(3)}</th>`;
+                for (let c = 0; c < table.N_C; c++) {
+                    try {
+                        const value = table.getValue(r, c, 0); // Get first value in cell
+                        html += `<td>${value.toFixed(6)}</td>`;
+                    } catch (error) {
+                        html += `<td>N/A</td>`;
+                    }
+                }
+                html += '</tr>';
+            }
+            html += '</tbody>';
+            html += '</table>';
+            html += '</div></div>';
+            
+            if (table.N_R > 50 && !showAll) {
+                html += `<p><em>Showing first 50 rows of ${table.N_R} total rows.</em></p>`;
+            } else if (showAll && table.N_R > 50) {
+                html += `<p><em>Showing all ${table.N_R} rows.</em></p>`;
+            }
+        }
+    } else {
+        html += '<p>No data to display.</p>';
+    }
+    
+    opatTableDataContent.innerHTML = html;
+    
+    // Auto-switch to Data Explorer tab when displaying data
+    const explorerTab = document.querySelector('[data-tab="opat-explorer-tab"]');
+    if (explorerTab) {
+        explorerTab.click();
+    }
+    
+    // Update table heights after table is rendered
+    setTimeout(() => {
+        if (window.updateTableHeights) {
+            window.updateTableHeights();
+        }
+    }, 50);
+}
diff --git a/electron/styles.css b/electron/styles.css
index eaf9f20..2a55dfc 100644
--- a/electron/styles.css
+++ b/electron/styles.css
@@ -504,18 +504,403 @@ body.dark-mode .info-button:hover {
   flex-direction: column;
   overflow: hidden;
   min-width: 0;
-  padding: 0;
+  padding: 20px;
 }
 
 #welcome-screen {
   display: flex;
   flex-direction: column;
+  height: 100%;
+  overflow-y: auto;
+  background: linear-gradient(135deg, #f8fafc 0%, #e2e8f0 100%);
+}
+
+.welcome-hero {
+  display: flex;
   justify-content: center;
   align-items: center;
-  height: 100%;
+  min-height: 300px;
+  background: linear-gradient(135deg, #1e293b 0%, #334155 100%);
+  color: white;
+  margin-bottom: 2rem;
+}
+
+.welcome-logo {
   text-align: center;
-  color: var(--text-light);
-  padding: 20px;
+}
+
+.star-icon-large {
+  font-size: 4rem;
+  color: #fbbf24;
+  margin-bottom: 1rem;
+  text-shadow: 0 0 20px rgba(251, 191, 36, 0.5);
+}
+
+.welcome-title {
+  font-size: 3.5rem;
+  font-weight: 700;
+  margin: 0;
+  letter-spacing: 0.1em;
+  background: linear-gradient(45deg, #fbbf24, #f59e0b);
+  -webkit-background-clip: text;
+  -webkit-text-fill-color: transparent;
+  background-clip: text;
+}
+
+.welcome-subtitle {
+  font-size: 1.2rem;
+  margin: 0.5rem 0 0 0;
+  color: #cbd5e1;
+  font-weight: 300;
+}
+
+.welcome-content {
+  flex: 1;
+  padding: 0 3rem 3rem 3rem;
+  max-width: 1200px;
+  margin: 0 auto;
+  width: 100%;
+}
+
+.welcome-section h2 {
+  color: #1e293b;
+  font-size: 2rem;
+  margin-bottom: 1rem;
+  text-align: center;
+}
+
+.welcome-section p {
+  color: #64748b;
+  font-size: 1.1rem;
+  text-align: center;
+  margin-bottom: 2rem;
+}
+
+.feature-grid {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
+  gap: 1.5rem;
+  margin-bottom: 3rem;
+}
+
+.feature-card {
+  display: flex;
+  align-items: flex-start;
+  gap: 1rem;
+  padding: 1.5rem;
+  background: white;
+  border-radius: 12px;
+  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
+  transition: all 0.3s ease;
+  border: 1px solid #e2e8f0;
+}
+
+.feature-card:hover {
+  transform: translateY(-2px);
+  box-shadow: 0 8px 25px -5px rgba(0, 0, 0, 0.15);
+}
+
+.feature-icon {
+  width: 48px;
+  height: 48px;
+  border-radius: 12px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  color: white;
+  font-weight: bold;
+  font-size: 1.2rem;
+  flex-shrink: 0;
+}
+
+.feature-info h3 {
+  color: #1e293b;
+  font-size: 1.2rem;
+  margin: 0 0 0.5rem 0;
+  font-weight: 600;
+}
+
+.feature-info p {
+  color: #64748b;
+  font-size: 0.95rem;
+  margin: 0;
+  line-height: 1.5;
+  text-align: left;
+}
+
+.welcome-tips {
+  background: white;
+  padding: 2rem;
+  border-radius: 12px;
+  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
+  border: 1px solid #e2e8f0;
+}
+
+.welcome-tips h3 {
+  color: #1e293b;
+  font-size: 1.4rem;
+  margin: 0 0 1rem 0;
+  font-weight: 600;
+}
+
+.welcome-tips ul {
+  color: #64748b;
+  font-size: 1rem;
+  line-height: 1.6;
+  margin: 0;
+  padding-left: 1.5rem;
+}
+
+.welcome-tips li {
+  margin-bottom: 0.5rem;
+}
+
+/* Category-specific home screens */
+.home-screen {
+  display: flex;
+  flex-direction: column;
+  height: 100%;
+  overflow-y: auto;
+}
+
+.category-hero {
+  display: flex;
+  justify-content: center;
+  align-items: center;
+  min-height: 250px;
+  background: linear-gradient(135deg, #1e293b 0%, #334155 100%);
+  color: white;
+  margin-bottom: 2rem;
+}
+
+.category-hero-content {
+  text-align: center;
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 1rem;
+}
+
+.category-icon-large {
+  width: 80px;
+  height: 80px;
+  border-radius: 20px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  color: white;
+  font-weight: bold;
+  font-size: 2.5rem;
+  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.3);
+}
+
+.category-title {
+  font-size: 2.5rem;
+  font-weight: 700;
+  margin: 0;
+  color: white;
+}
+
+.category-subtitle {
+  font-size: 1.1rem;
+  margin: 0;
+  color: #cbd5e1;
+  font-weight: 300;
+}
+
+.category-content {
+  flex: 1;
+  padding: 0 3rem 3rem 3rem;
+  max-width: 1000px;
+  margin: 0 auto;
+  width: 100%;
+}
+
+.feature-section h2 {
+  color: #1e293b;
+  font-size: 1.8rem;
+  margin-bottom: 1.5rem;
+  text-align: center;
+}
+
+.action-cards {
+  display: grid;
+  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
+  gap: 1.5rem;
+  margin-bottom: 3rem;
+}
+
+.action-card {
+  padding: 2rem;
+  background: white;
+  border-radius: 12px;
+  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
+  transition: all 0.3s ease;
+  border: 1px solid #e2e8f0;
+  text-align: center;
+}
+
+.action-card:hover {
+  transform: translateY(-4px);
+  box-shadow: 0 12px 32px -8px rgba(0, 0, 0, 0.15);
+}
+
+.action-card h3 {
+  color: #1e293b;
+  font-size: 1.3rem;
+  margin: 0 0 1rem 0;
+  font-weight: 600;
+}
+
+.action-card p {
+  color: #64748b;
+  font-size: 1rem;
+  margin: 0;
+  line-height: 1.6;
+}
+
+.info-section {
+  background: white;
+  padding: 2rem;
+  border-radius: 12px;
+  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
+  border: 1px solid #e2e8f0;
+}
+
+.info-section h3 {
+  color: #1e293b;
+  font-size: 1.4rem;
+  margin: 0 0 1rem 0;
+  font-weight: 600;
+}
+
+.info-section p {
+  color: #64748b;
+  font-size: 1rem;
+  line-height: 1.6;
+  margin: 0;
+}
+
+/* Dark mode support for home screens */
+body.dark-mode .home-screen {
+  background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
+}
+
+body.dark-mode .category-hero {
+  background: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
+}
+
+body.dark-mode .feature-section h2,
+body.dark-mode .category-title {
+  color: #f1f5f9;
+}
+
+body.dark-mode .category-subtitle {
+  color: #94a3b8;
+}
+
+body.dark-mode .action-card,
+body.dark-mode .info-section,
+body.dark-mode .feature-card,
+body.dark-mode .welcome-tips {
+  background: #1e293b;
+  border-color: #334155;
+}
+
+body.dark-mode .action-card h3,
+body.dark-mode .info-section h3,
+body.dark-mode .feature-info h3,
+body.dark-mode .welcome-tips h3 {
+  color: #f1f5f9;
+}
+
+body.dark-mode .action-card p,
+body.dark-mode .info-section p,
+body.dark-mode .feature-info p,
+body.dark-mode .welcome-tips ul {
+  color: #94a3b8;
+}
+
+body.dark-mode .welcome-section h2 {
+  color: #f1f5f9;
+}
+
+body.dark-mode .welcome-section p {
+  color: #94a3b8;
+}
+
+/* Custom scrollbar styling for all views */
+::-webkit-scrollbar {
+  width: 8px;
+  height: 8px;
+}
+
+::-webkit-scrollbar-track {
+  background: #f1f5f9;
+  border-radius: 4px;
+}
+
+::-webkit-scrollbar-thumb {
+  background: #cbd5e1;
+  border-radius: 4px;
+  transition: background-color 0.2s ease;
+}
+
+::-webkit-scrollbar-thumb:hover {
+  background: #94a3b8;
+}
+
+::-webkit-scrollbar-corner {
+  background: #f1f5f9;
+}
+
+/* Dark mode scrollbar styling */
+body.dark-mode ::-webkit-scrollbar-track {
+  background: #1e293b;
+}
+
+body.dark-mode ::-webkit-scrollbar-thumb {
+  background: #475569;
+}
+
+body.dark-mode ::-webkit-scrollbar-thumb:hover {
+  background: #64748b;
+}
+
+body.dark-mode ::-webkit-scrollbar-corner {
+  background: #1e293b;
+}
+
+/* Specific scrollbar styling for table containers */
+.opat-table-container ::-webkit-scrollbar {
+  width: 10px;
+  height: 10px;
+}
+
+.opat-table-container ::-webkit-scrollbar-track {
+  background: #f8fafc;
+  border-radius: 5px;
+}
+
+.opat-table-container ::-webkit-scrollbar-thumb {
+  background: #e2e8f0;
+  border-radius: 5px;
+}
+
+.opat-table-container ::-webkit-scrollbar-thumb:hover {
+  background: #cbd5e1;
+}
+
+body.dark-mode .opat-table-container ::-webkit-scrollbar-track {
+  background: #0f172a;
+}
+
+body.dark-mode .opat-table-container ::-webkit-scrollbar-thumb {
+  background: #334155;
+}
+
+body.dark-mode .opat-table-container ::-webkit-scrollbar-thumb:hover {
+  background: #475569;
 }
 
 #welcome-screen h1 {
@@ -1178,11 +1563,11 @@ body.dark-mode .fill-header p {
 }
 
 #fill-progress-container {
-    margin-top: 20px;
-    padding: 16px;
-    background-color: var(--sidebar-bg);
+    margin-bottom: 20px;
+    padding: 20px 30px;
+    background-color: #f8f9fa;
     border-radius: 8px;
-    border: 1px solid var(--border-color);
+    border: 1px solid #e9ecef;
 }
 
 #fill-progress-content {
@@ -1530,6 +1915,346 @@ body.dark-mode .info-tab-pane a {
   line-height: 1.6;
 }
 
+/* OPAT File Inspector Styling */
+#opat-tab-content {
+  padding: 20px;
+  height: calc(100vh - 200px);
+  overflow-y: auto;
+  display: flex;
+  flex-direction: column;
+}
+
+#opat-tab-content .tab-pane {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+}
+
+.opat-table-container {
+  flex: 1;
+  display: flex;
+  flex-direction: column;
+  min-height: 0;
+  height: calc(100vh - 450px);
+}
+
+.table-scroll-wrapper {
+  width: 100%;
+  height: 100%;
+  min-height: 300px;
+  overflow: auto;
+  flex: 1;
+}
+
+#opat-tab-content .tab-pane {
+  padding: 0;
+}
+.opat-section {
+  margin-bottom: 20px;
+  padding: 16px;
+  background: white;
+  border: 1px solid #e5e7eb;
+  border-radius: 8px;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+}
+
+body.dark-mode .opat-section {
+  background: #4b5563;
+  border: 1px solid #6b7280;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
+}
+
+.opat-label {
+  display: block;
+  font-size: 0.9rem;
+  font-weight: 500;
+  color: #374151;
+  margin-bottom: 8px;
+}
+
+body.dark-mode .opat-label {
+  color: #f3f4f6;
+}
+
+.opat-file-input {
+  display: none;
+}
+
+.opat-content-wrapper {
+  margin-top: 20px;
+}
+
+.opat-info-section {
+  margin: 0 20px 24px 20px;
+  padding: 20px 30px;
+  background: white;
+  border: 1px solid #e5e7eb;
+  border-radius: 8px;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
+}
+
+body.dark-mode .opat-info-section {
+  background: #4b5563;
+  border: 1px solid #6b7280;
+  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
+}
+
+.opat-section-title {
+  font-size: 1.1rem;
+  font-weight: 600;
+  color: #1f2937;
+  margin: 0 0 12px 0;
+  padding-bottom: 8px;
+  border-bottom: 1px solid #e5e7eb;
+}
+
+body.dark-mode .opat-section-title {
+  color: #f3f4f6;
+  border-bottom: 1px solid #6b7280;
+}
+
+.opat-info-content {
+  font-size: 0.85rem;
+  color: #6b7280;
+  line-height: 1.5;
+}
+
+body.dark-mode .opat-info-content {
+  color: #d1d5db;
+}
+
+.opat-tags-list {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+  max-height: 200px;
+  overflow-y: auto;
+}
+
+.opat-tags-list li {
+  padding: 6px 12px;
+  margin: 4px 0;
+  background: #f9fafb;
+  border: 1px solid #e5e7eb;
+  border-radius: 6px;
+  font-size: 0.85rem;
+  font-family: monospace;
+  color: #059669;
+}
+
+body.dark-mode .opat-tags-list li {
+  background: #374151;
+  border: 1px solid #4b5563;
+  color: #10b981;
+}
+
+.opat-selector-group {
+  margin-bottom: 16px;
+}
+
+.opat-select {
+  width: 100%;
+  padding: 8px 12px;
+  background: white;
+  border: 1px solid #d1d5db;
+  border-radius: 6px;
+  font-size: 0.9rem;
+  color: #374151;
+  cursor: pointer;
+}
+
+body.dark-mode .opat-select {
+  background: #374151;
+  border: 1px solid #4b5563;
+  color: #f3f4f6;
+}
+
+.opat-tables-display {
+  max-height: 300px;
+  overflow-y: auto;
+}
+
+.opat-table-info {
+  padding: 12px;
+  margin: 8px 0;
+  background: #f8f9fa;
+  border: 1px solid #e5e7eb;
+  border-radius: 6px;
+  cursor: pointer;
+  transition: all 0.2s ease;
+}
+
+.opat-table-info:hover {
+  background: #e5e7eb;
+  border-color: #3b82f6;
+}
+
+body.dark-mode .opat-table-info {
+  background: #374151;
+  border: 1px solid #4b5563;
+}
+
+body.dark-mode .opat-table-info:hover {
+  background: #4b5563;
+  border-color: #3b82f6;
+}
+
+.opat-table-tag {
+  font-weight: 600;
+  color: #059669;
+  font-family: monospace;
+  margin-bottom: 4px;
+}
+
+body.dark-mode .opat-table-tag {
+  color: #10b981;
+}
+
+.opat-table-details {
+  font-size: 0.8rem;
+  color: #6b7280;
+  line-height: 1.4;
+}
+
+body.dark-mode .opat-table-details {
+  color: #9ca3af;
+}
+
+.opat-table-viewer {
+  max-height: 400px;
+  overflow: auto;
+  border: 1px solid #e5e7eb;
+  border-radius: 6px;
+  background: white;
+}
+
+body.dark-mode .opat-table-viewer {
+  border: 1px solid #4b5563;
+  background: #374151;
+}
+
+.opat-placeholder {
+  padding: 20px;
+  text-align: center;
+  color: #9ca3af;
+  font-style: italic;
+  margin: 0;
+}
+
+body.dark-mode .opat-placeholder {
+  color: #6b7280;
+}
+
+.opat-data-table {
+  width: 100%;
+  border-collapse: collapse;
+  font-size: 0.8rem;
+  font-family: monospace;
+}
+
+.opat-data-table th,
+.opat-data-table td {
+  padding: 6px 8px;
+  border: 1px solid #e5e7eb;
+  text-align: center;
+}
+
+body.dark-mode .opat-data-table th,
+body.dark-mode .opat-data-table td {
+  border: 1px solid #4b5563;
+}
+
+.opat-data-table th {
+  background: #f8f9fa;
+  font-weight: 600;
+  color: #374151;
+  position: sticky;
+  top: 0;
+  z-index: 1;
+}
+
+body.dark-mode .opat-data-table th {
+  background: #4b5563;
+  color: #f3f4f6;
+}
+
+.opat-data-table th.row-header {
+    background-color: #f8fafc;
+    font-weight: 600;
+    text-align: right;
+    padding-right: 12px;
+}
+
+body.dark-mode .opat-data-table th.row-header {
+  background: #4b5563;
+}
+
+.table-controls {
+    margin: 1rem 0;
+    text-align: center;
+}
+
+.show-all-btn, .show-less-btn {
+    background-color: #3b82f6;
+    color: white;
+    border: none;
+    padding: 8px 16px;
+    border-radius: 6px;
+    cursor: pointer;
+    font-size: 0.9rem;
+    font-weight: 500;
+    transition: background-color 0.2s ease;
+}
+
+.show-all-btn:hover, .show-less-btn:hover {
+    background-color: #2563eb;
+}
+
+.show-less-btn {
+    background-color: #6b7280;
+}
+
+.show-less-btn:hover {
+    background-color: #4b5563;
+}
+
+.opat-data-table .corner-cell {
+  position: sticky;
+  top: 0;
+  left: 0;
+  z-index: 2;
+  background: #e5e7eb;
+}
+
+body.dark-mode .opat-data-table .corner-cell {
+  background: #6b7280;
+}
+
+.opat-table-title {
+  padding: 12px 16px;
+  margin: 0;
+  font-size: 1rem;
+  font-weight: 600;
+  color: #1f2937;
+  background: #f8f9fa;
+  border-bottom: 1px solid #e5e7eb;
+}
+
+body.dark-mode .opat-table-title {
+  color: #f3f4f6;
+  background: #4b5563;
+  border-bottom: 1px solid #6b7280;
+}
+
+.opat-table-tag-highlight {
+  color: #059669;
+  font-family: monospace;
+}
+
+body.dark-mode .opat-table-tag-highlight {
+  color: #10b981;
+}
+
 .info-tab-pane ul {
   margin: 12px 0;
   padding-left: 20px;