:root {
            --bg-sidebar: #121417;
            --bg-viewer: #1a1d21;
            --text-main: #d1d5db;
            --accent: #4a90e2;
            --border: rgba(255, 255, 255, 0.1);
        }

        * { margin: 0; padding: 0; box-sizing: border-box; }

        body {
            font-family: 'Inter', sans-serif;
            background-color: var(--bg-viewer);
            height: 100vh;
            overflow: hidden;
            transition: background-color 0.3s ease;
        }

        /* Progress Bar */
        #progress-container {
            position: fixed; top: 0; left: 0; width: 100%; height: 3px;
            background: rgba(255, 255, 255, 0.1); z-index: 3000;
        }
        #progress-bar { height: 100%; background: var(--accent); width: 0%; transition: width 0.3s; }

        /* Navbar */
        .mobile-navbar {
            height: 56px;
            background: var(--bg-sidebar);
            display: flex;
            align-items: center;
            padding: 0 1rem;
            box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
            position: relative;
            z-index: 2000;
            transition: background-color 0.3s ease;
            border-bottom: 1px solid var(--border);
        }
        .mobile-navbar .brand { color: var(--text-main); font-size: 1.1rem; font-weight: 600; flex: 1; }

        .burger-button {
            background: none; border: none; width: 40px; height: 40px; cursor: pointer;
            display: flex; flex-direction: column; justify-content: center; align-items: center; gap: 5px;
            position: relative; z-index: 2001;
        }
        
        @media screen and (min-width: 1025px) { .burger-button { display: none; } }

        .burger-button span { display: block; width: 24px; height: 2px; background: var(--text-main); transition: all 0.3s; }
        .burger-button.is-active span:nth-child(1) { transform: rotate(45deg) translate(5px, 5px); }
        .burger-button.is-active span:nth-child(2) { opacity: 0; }
        .burger-button.is-active span:nth-child(3) { transform: rotate(-45deg) translate(7px, -7px); }

        /* Sidebar Overlay */
        .sidebar-overlay {
            display: none; position: fixed; top: 56px; left: 0; width: 100%; height: calc(100% - 56px);
            background: rgba(0, 0, 0, 0.5); z-index: 1000; opacity: 0; transition: opacity 0.3s;
        }
        .sidebar-overlay.is-active { display: block; opacity: 1; }

        /* Main Container */
        .main-container { display: flex; height: calc(100vh - 56px); width: 100%; position: relative; }

        /* Sidebar */
        .sidebar {
            width: 375px; 
            background: var(--bg-sidebar); 
            color: var(--text-main); 
            display: flex; 
            flex-direction: column;
            height: 100%; 
            position: relative; 
            z-index: 1500; 
            border-right: 1px solid var(--border);
            transition: transform 0.3s ease, background-color 0.3s ease;
        }

        .sidebar-inner { flex: 1; overflow-y: auto; padding: 2rem 0; }
        .library-header { padding: 0 1.5rem; font-size: 0.75rem; color: #888; letter-spacing: 2px; margin-bottom: 2rem; font-weight: 600; }

        /* Book Items */
        .book-item-wrapper { list-style: none; }
        .book-link-container {
            display: flex !important; align-items: flex-start; padding: 1rem 1.5rem !important;
            text-decoration: none; transition: background 0.2s; cursor: pointer;
            color: var(--text-main) !important;
        }
        .book-link-container:hover { background: rgba(128, 128, 128, 0.1); }
        .book-link-container.is-active { background: rgba(74, 144, 226, 0.1); border-right: 3px solid var(--accent); }

        .download-action { margin-right: 1.25rem; opacity: 0.6; padding-top: 4px; color: inherit; }
        .book-info { flex: 1; text-align: right; }
        .book-title { display: block; font-size: 0.95rem; font-weight: 600; line-height: 1.4; text-transform: uppercase; color: inherit; }
        .book-author { display: block; font-size: 0.85rem; opacity: 0.7; margin-top: 4px; color: inherit; }

        /* Viewer Area */
        .viewer-column {
            flex: 1; height: 100%; overflow-y: auto; background: var(--bg-viewer);
            display: flex; flex-direction: column; align-items: center;
            transition: background-color 0.3s ease;
        }
        #viewer { width: 100%; max-width: 850px; padding: 4rem 2rem; min-height: 100%; }

        /* Theme Switcher - Fixed for Mobile */
        .theme-switcher { 
            padding: 1rem; 
            display: flex; 
            justify-content: center; 
            align-items: center;
            gap: 1.25rem; 
            border-top: 1px solid var(--border); 
            background: var(--bg-sidebar);
            position: relative;
            z-index: 1600;
            flex-shrink: 0; /* Prevents shrinking */
        }
        .theme-dot { 
            width: 32px; 
            height: 32px; 
            border-radius: 50%; 
            cursor: pointer; 
            border: 2px solid rgba(128,128,128,0.3); 
            transition: 0.2s;
            display: block;
        }
        .theme-dot:hover { transform: scale(1.1); border-color: var(--accent); }

        /* Mobile Layout Adjustments */
        @media screen and (max-width: 1024px) {
            .sidebar { position: fixed; left: 0; transform: translateX(-100%); width: 280px; }
            .sidebar.is-mobile-active { transform: translateX(0); }
            .theme-switcher { gap: 1rem; padding: 1.25rem 0.5rem; }
            .theme-dot { width: 38px; height: 38px; } /* Slightly larger for easier touch */
        }

        /* Theme Specific Settings */
        body.theme-dark {
            --bg-sidebar: #121417;
            --bg-viewer: #1a1d21;
            --text-main: #d1d5db;
            --border: rgba(255, 255, 255, 0.1);
        }
        body.theme-sepia {
            --bg-sidebar: #eadecd;
            --bg-viewer: #f4ecd8;
            --text-main: #5f4b32;
            --border: rgba(0, 0, 0, 0.1);
        }
        body.theme-light {
            --bg-sidebar: #f5f5f5;
            --bg-viewer: #ffffff;
            --text-main: #333333;
            --border: rgba(0, 0, 0, 0.05);
        }