:root {
            --primary-bg: #f4f6f9;
            --secondary-bg: #ffffff;
            --text-color: #212529;
            --primary-color: #007bff;
            --secondary-color: #6c757d;
            --success-color: #28a745;
            --danger-color: #dc3545;
            --warning-color: #ffc107;
            --info-color: #17a2b8;
            --border-radius: 8px;
            --box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
        }
        body {
            font-family: 'Segoe UI', Arial, sans-serif;
            background-color: var(--primary-bg);
            color: var(--text-color);
            margin: 0;
            padding: 15px;
            transition: box-shadow 0.2s, padding-top 0.3s ease; /* Thêm hiệu ứng trượt cho body khi có thông báo */
            min-height: 100vh;
        }

        /* --- REWARD SYSTEM STYLES --- */
        .border-correct {
            box-shadow: inset 0 0 60px rgba(40, 167, 69, 0.6) !important;
            transition: box-shadow 0.1s ease-out;
        }

        .border-wrong {
            box-shadow: inset 0 0 60px rgba(220, 53, 69, 0.6) !important;
            animation: shake 0.4s cubic-bezier(.36,.07,.19,.97) both;
        }

        @keyframes shake {
            0%, 100% { transform: translateX(0); }
            10%, 30%, 50%, 70%, 90% { transform: translateX(-5px); }
            20%, 40%, 60%, 80% { transform: translateX(5px); }
        }

        .rainbow-text {
            background: linear-gradient(to right, #d32f2f, #f57c00, #fbc02d, #388e3c, #1976d2, #7b1fa2);
            -webkit-background-clip: text;
            background-clip: text;
            color: transparent;
            animation: rainbow_anim 1s linear infinite;
            font-weight: 900 !important;
        }
        @keyframes rainbow_anim { to { background-position: 200% center; } }

        #reward-overlay {
            position: fixed; top: 0; left: 0; width: 100%; height: 100%;
            pointer-events: none; /* Click through */
            z-index: 1500; /* Above most things, below floating bar/modals if needed */
            display: flex; flex-direction: column; align-items: center; justify-content: center;
        }

        #reward-status-text {
            font-size: 3rem; font-weight: 800; text-transform: uppercase;
            text-align: center; text-shadow: 2px 2px 4px rgba(0,0,0,0.3);
            opacity: 0; transform: scale(0.5);
            transition: all 0.3s cubic-bezier(0.175, 0.885, 0.32, 1.275);
            padding: 10px 20px; background: rgba(255,255,255,0.8);
            border-radius: 15px; backdrop-filter: blur(2px);
        }
        #reward-status-text.show { opacity: 1; transform: scale(1); }

        #reward-badge {
            position: fixed; top: 20px; left: 50%; transform: translateX(-50%);
            padding: 8px 25px; border-radius: 30px;
            background: #fff; border: 2px solid #ddd;
            font-weight: bold; font-size: 1.2rem; color: #555;
            box-shadow: 0 4px 6px rgba(0,0,0,0.1);
            z-index: 1501; opacity: 0; transition: opacity 0.3s;
        }
        #reward-badge.show { opacity: 1; }
        /* --------------------------- */

        .container {
            max-width: 800px;
            margin: auto;
            background-color: var(--secondary-bg);
            padding: 20px;
            border-radius: var(--border-radius);
            box-shadow: var(--box-shadow);
            overflow-y: auto;
            max-height: 95vh;
            transition: padding-bottom 0.3s;
            position: relative; z-index: 10; /* Ensure container is above body background */
        }
        .container.pb-safe {
            padding-bottom: 100px !important;
        }

        .screen { display: none; }
        .screen.active { display: block; }
        
        h1, h2, h3 { text-align: center; color: var(--primary-color); }
        
        .button-group { display: grid; grid-template-columns: 1fr; gap: 10px; margin-bottom: 20px; }
        .btn {
            padding: 12px; font-size: 16px; font-weight: bold; color: white;
            background-color: var(--primary-color); border: none; border-radius: var(--border-radius);
            cursor: pointer; text-align: center; transition: background-color 0.2s, transform 0.1s;
        }
        .btn:active { transform: translateY(2px); }
        .btn:hover { background-color: #0056b3; }
        .btn-secondary { background-color: var(--secondary-color); }
        .btn-secondary:hover { background-color: #5a6268; }
        .btn-danger { background-color: var(--danger-color); }
        .btn-danger:hover { background-color: #c82333; }
        .btn-warning { background-color: var(--warning-color); }
        .btn-warning:hover { background-color: #e0a800; }
        .btn-success { background-color: var(--success-color); }
        .btn-success:hover { background-color: #218838; }
        
        /* Sidebar Styles */
        .sidebar { width: 260px; max-height: 80vh; overflow-y: auto; position: fixed; top: 0; left: 0; height: 100%; background-color: var(--secondary-bg); box-shadow: var(--box-shadow); transition: transform 0.3s ease; z-index: 900; }
        .pill-container { display: flex; flex-wrap: wrap; gap: 8px; padding: 8px; }
        .main-content { transition: all 0.3s ease; padding: 15px; }
        .with-sidebar { margin-left: 260px; width: calc(100% - 260px); }
        .full { margin-left: 0; width: 100%; }
        
        /* Modal Styles */
        .modal { display: none; position: fixed; top: 0; left: 0; width: 100%; height: 100%; background-color: rgba(0, 0, 0, 0.5); z-index: 1000; }
        .modal-content { background-color: var(--secondary-bg); margin: 5% auto; padding: 20px; border-radius: var(--border-radius); width: 95%; max-width: 800px; max-height: 90vh; overflow-y: auto; box-shadow: var(--box-shadow); position: relative; }
        #statisticsModal .modal-content { max-width: 500px; }
        .modal-content.large-search-open { margin-top: 0.5%; padding-top: 150px; }
        
        /* Comparison Styles */
        .comparison-question { margin-bottom: 25px; padding-bottom: 15px; border-bottom: 2px solid #ccc; }
        .comparison-question:last-of-type { border-bottom: none; }
        .comparison-question-text { margin-bottom: 15px; white-space: pre-wrap; }
        .options-comparison-wrapper { display: flex; flex-direction: row; gap: 15px; }
        .options-column { flex: 1; min-width: 48%; border: 1px solid #e0e0e0; border-radius: var(--border-radius); padding: 10px; background-color: #fdfdfd; }
        .options-column h5 { margin-top: 0; text-align: center; border-bottom: 1px solid #eee; padding-bottom: 5px; margin-bottom: 10px; font-size: 16px; }
        .option-item { padding: 4px; margin: 3px 0; border-radius: 4px; }
        
        /* Search & Floating Menu Styles */
        #comparison-menu-btn { position: fixed; top: 20px; right: 20px; width: 40px; height: 40px; background-color: var(--primary-color); border-radius: 50%; cursor: pointer; z-index: 2102; display: flex; flex-direction: column; justify-content: center; align-items: center; gap: 4px; box-shadow: 0 2px 5px rgba(0,0,0,0.2); }
        #comparison-menu-btn .bar { width: 20px; height: 2px; background-color: white; transition: all 0.3s; }
        .search-menu { background-color: #fff; box-shadow: 0 5px 15px rgba(0,0,0,0.2); z-index: 2101; box-sizing: border-box; position: absolute; }
        .search-menu h4 { margin-top: 0; color: var(--primary-color); }
        .search-menu .input-group { margin-bottom: 15px; display: flex; align-items: center; }
        .search-menu .input-group label { width: 60px; }
        .search-menu input { flex: 1; padding: 8px; border: 1px solid #ccc; border-radius: 4px; }
        .search-menu .icon-btn { background: none; border: none; cursor: pointer; font-size: 24px; }
        .search-menu .clear-btn { border: 1px solid #ccc; border-radius: 4px; padding: 2px 8px; cursor: pointer; }
        #small-search-menu { top: 65px; right: 20px; width: 300px; height: auto; padding: 15px; border-radius: var(--border-radius); transform-origin: top right; transition: transform 0.2s ease-out, opacity 0.2s; transform: scale(0.95); opacity: 0; pointer-events: none; }
        #small-search-menu.open { transform: scale(1); opacity: 1; pointer-events: auto; }
        #large-search-menu { top: 0; left: 0; width: 100%; height: auto; display: flex; flex-direction: column; padding: 15px 65px 15px 15px; border-bottom: 1px solid #eee; transition: transform 0.3s ease-in-out; transform: translateY(-110%); }
        #large-search-menu.open { transform: translateY(0); }
        #large-search-menu .search-controls { display: flex; width: 100%; gap: 10px; align-items: center; margin-top: 45px; }
        #large-search-menu .input-group { flex: 1; margin-bottom: 0; }
        #large-search-results { font-weight: bold; color: var(--success-color); margin-top: 10px; }
        .nav-buttons { display: flex; justify-content: center; gap: 10px; margin-top: 10px; }
        mark { background-color: #ffc107; padding: 0 2px; }
        mark.current-match { background-color: #ff5722; color: white; }
        
        #comparison-help-btn { position: fixed; top: 20px; left: 20px; width: 40px; height: 40px; background-color: var(--secondary-color); border-radius: 50%; cursor: pointer; z-index: 2102; display: flex; justify-content: center; align-items: center; font-size: 24px; font-weight: bold; color: white; box-shadow: 0 2px 5px rgba(0,0,0,0.2); }
        #helpModal .modal-content ul { list-style-type: none; padding: 0; }
        #helpModal .modal-content li { margin-bottom: 15px; line-height: 1.6; }
        #helpModal .modal-content .icon { display: inline-block; width: 20px; text-align: center; margin-right: 10px; }
        #statistics-legend { margin-top: 15px; font-size: 16px; line-height: 1.6; text-align: center; border-top: 1px solid #eee; padding-top: 15px; }
        #statistics-chart { min-height: 300px; color: #333; }

        /* === FLOATING ACTION BAR === */
        .floating-action-bar {
            position: fixed; bottom: 0; left: 0; width: 100%;
            background: rgba(255, 255, 255, 0.95); backdrop-filter: blur(5px);
            border-top: 1px solid #e0e0e0; padding: 15px;
            box-shadow: 0 -4px 15px rgba(0,0,0,0.1); z-index: 2000;
            display: flex; justify-content: center; animation: slideUp 0.3s ease-out;
        }
        @keyframes slideUp { from { transform: translateY(100%); } to { transform: translateY(0); } }
        .floating-action-bar .btn {
            width: 100%; max-width: 800px; border-radius: 12px;
            font-size: 18px; padding: 15px;
            box-shadow: 0 4px 6px rgba(50, 50, 93, 0.11), 0 1px 3px rgba(0, 0, 0, 0.08);
        }

        /* === QUIZ STYLES === */
        .options-container label { display: flex; align-items: flex-start; margin-bottom: 10px; padding: 12px; border: 1px solid #ddd; border-radius: 5px; cursor: pointer; transition: background-color 0.2s; }
        .options-container label input { margin-top: 4px; flex-shrink: 0; }
        .options-container label:hover { background-color: #f0f0f0; }
        .tf-option { display: flex; align-items: center; justify-content: space-between; padding: 12px; border: 1px solid #ddd; border-radius: var(--border-radius); margin-bottom: 10px; }
        .tf-btn { padding: 8px 16px; border: 1px solid var(--secondary-color); background-color: white; color: var(--secondary-color); border-radius: 20px; cursor: pointer; font-weight: bold; transition: all 0.2s; min-width: 80px; text-align: center; }
        .tf-btn.selected-true { background-color: var(--success-color); color: white; border-color: var(--success-color); }
        .tf-btn.selected-false { background-color: var(--danger-color); color: white; border-color: var(--danger-color); }
        
        /* PROGRESS BAR STYLES */
        .progress-wrapper { margin-bottom: 20px; }
        .progress-bar-container { display: flex; height: 10px; background-color: #e9ecef; border-radius: 5px; overflow: hidden; width: 100%; margin-bottom: 8px; }
        .progress-segment { flex: 1; border-right: 1px solid #fff; transition: background-color 0.3s; }
        .progress-segment:last-child { border-right: none; }
        .progress-segment.correct { background-color: var(--success-color) !important; }
        .progress-segment.incorrect { background-color: var(--danger-color) !important; }
        .progress-segment.active { background-color: #adb5bd; }
        
        .progress-info { 
            display: flex; 
            justify-content: center;
            gap: 15px;
            font-size: 1rem; 
            color: var(--secondary-color);
            flex-wrap: wrap; 
            align-items: center;
        }

        /* SETTINGS */
        #settings-icon-container { position: absolute; top: 15px; right: 20px; cursor: pointer; z-index: 100; padding: 5px; }
        .hamburger-line { width: 25px; height: 3px; background-color: var(--secondary-color); margin: 5px 0; transition: 0.3s; }
        #settings-panel { display: none; position: absolute; top: 50px; right: 20px; background-color: var(--secondary-bg); border-radius: var(--border-radius); box-shadow: var(--box-shadow); padding: 15px; z-index: 99; min-width: 250px; border: 1px solid #eee; }
        .settings-row { display: flex; align-items: center; justify-content: space-between; margin-bottom: 12px; }
        .switch { position: relative; display: inline-block; width: 44px; height: 24px; }
        .switch input { opacity: 0; width: 0; height: 0; }
        .slider { position: absolute; cursor: pointer; top: 0; left: 0; right: 0; bottom: 0; background-color: #ccc; transition: .4s; border-radius: 34px; }
        .slider:before { position: absolute; content: ""; height: 16px; width: 16px; left: 4px; bottom: 4px; background-color: white; transition: .4s; border-radius: 50%; }
        input:checked + .slider { background-color: var(--primary-color); }
        input:checked + .slider:before { transform: translateX(20px); }