body {
            margin: 0;
            padding: 20px;
            background: linear-gradient(135deg, #1a4855 0%, #243b55 100%);
            min-height: 100vh;
            font-family: Arial, sans-serif;
            color: #333;
        }

        .header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 20px 40px;
            width: 100%;
            box-sizing: border-box;
            position: absolute;
            top: 0;
            left: 0;
        }

        .logo {
            font-size: 1.8em;
            font-weight: bold;
            color: white;
            text-decoration: none;
            text-shadow: 0 2px 4px rgba(0,0,0,0.2);
        }

        .home-link {
            color: white;
            text-decoration: none;
            font-size: 1.1em;
            font-weight: 500;
            transition: opacity 0.3s ease;
        }

        .home-link:hover {
            opacity: 0.8;
        }

        .quiz-container {
            max-width: 800px;
            margin: 80px auto 40px;
            padding: 30px;
            background: rgba(255, 255, 255, 0.95);
            border-radius: 20px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
        }

        .quiz-title {
            text-align: center;
            color: #2c3e50;
            margin-bottom: 40px;
            padding-bottom: 20px;
            border-bottom: 3px solid #e8e8e8;
            position: relative;
        }

        .quiz-title::after {
            font-size: 2em;
            position: absolute;
            bottom: -15px;
            left: 50%;
            transform: translateX(-50%);
            background: white;
            padding: 0 20px;
        }

        .quiz-title h1 {
            font-size: 2.5em;
            margin-bottom: 10px;
        }

        .quiz-title p {
            font-size: 1.1em;
            color: #666;
            max-width: 600px;
            margin: 0 auto;
            line-height: 1.6;
        }

        .question-container {
            background-color: white;
            padding: 30px;
            margin-bottom: 30px;
            border-radius: 12px;
            box-shadow: 0 2px 8px rgba(0,0,0,0.1);
            text-align: center;
            display: none;
            border: 1px solid #eaeaea;
            transition: all 0.3s ease;
        }

        .question-container.active {
            display: block;
        }

        .question-container:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 15px rgba(0,0,0,0.1);
        }

        .question {
            font-size: 1.2em;
            font-weight: bold;
            margin-bottom: 25px;
            color: #2c3e50;
            line-height: 1.4;
        }

        .choices {
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 12px;
            margin-bottom: 20px;
        }

        .choice-label {
            display: flex;
            align-items: center;
            padding: 12px 20px;
            width: 80%;
            max-width: 400px;
            background: linear-gradient(145deg, #ffffff, #f0f0f0);
            border: 1px solid #e0e0e0;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.3s ease;
            position: relative;
            overflow: hidden;
        }

        .choice-label:hover {
            background: linear-gradient(145deg, #f0f0f0, #e8e8e8);
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.05);
        }

        .choice-label input[type="radio"] {
            margin-right: 12px;
        }

        .submit-answer-btn {
            background: linear-gradient(145deg, #2c3e50, #34495e);
            padding: 12px 30px;
            border-radius: 25px;
            box-shadow: 0 4px 15px rgba(0,0,0,0.1);
            font-weight: 600;
            letter-spacing: 0.5px;
            color: white;
            border: none;
            cursor: pointer;
            transition: background-color 0.3s;
            margin: 15px auto;
        }

        .submit-answer-btn:hover {
            background: linear-gradient(145deg, #34495e, #2c3e50);
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(0,0,0,0.15);
        }

        .submit-answer-btn:disabled {
            background-color: #95a5a6;
            cursor: not-allowed;
        }

        .feedback {
            margin-top: 25px;
            padding: 20px;
            border-radius: 12px;
            text-align: center;
            display: none;
            animation: fadeIn 0.5s ease;
        }

        .correct {
            background-color: #d4edda;
            color: #155724;
            border: 1px solid #c3e6cb;
        }

        .incorrect {
            background-color: #f8d7da;
            color: #721c24;
            border: 1px solid #f5c6cb;
        }

        .justification {
            margin-top: 15px;
            font-style: italic;
            color: #666;
            line-height: 1.5;
            padding: 0 20px;
        }

        #score {
            text-align: center;
            font-size: 1.4em;
            font-weight: bold;
            margin: 30px 0;
            padding: 20px;
            background-color: white;
            border-radius: 8px;
            box-shadow: 0 2px 8px rgba(0,0,0,0.1);
        }

        /* Responsive design */
        @media (max-width: 600px) {
            .quiz-container {
                padding: 10px;
            }

            .question-container {
                padding: 20px;
            }

            .choice-label {
                width: 90%;
            }

            .quiz-title h1 {
                font-size: 2em;
            }
        }

        .progress-bars {
            background: linear-gradient(145deg, #ffffff, #f8f8f8);
            border: 1px solid #eaeaea;
            padding: 20px;
            margin: 20px 0;
            border-radius: 8px;
            box-shadow: 0 2px 8px rgba(0,0,0,0.1);
        }

        .progress-bar {
            height: 12px;
            border-radius: 6px;
            background: #f0f0f0;
            box-shadow: inset 0 1px 3px rgba(0,0,0,0.1);
            position: relative;
            margin-bottom: 15px;
        }

        .progress-fill {
            position: absolute;
            left: 0;
            top: 0;
            height: 100%;
            border-radius: 6px;
            transition: width 0.5s ease;
        }

        .progress-correct {
            background: linear-gradient(90deg, #28a745, #20c997);
        }

        .progress-incorrect {
            background: linear-gradient(90deg, #dc3545, #e74c3c);
        }

        .progress-label {
            font-size: 0.9em;
            color: #666;
            margin-bottom: 5px;
        }

        .concept-content {
            text-align: left;
            line-height: 1.6;
            color: #2c3e50;
            margin-bottom: 25px;
            padding: 25px;
            background: linear-gradient(145deg, #ffffff, #f8f8f8);
            border-radius: 15px;
            border: 1px solid #eaeaea;
        }

        .concept-content p {
            margin-bottom: 15px;
        }

        .concept-content h2 {
            font-size: 1.6em;
            color: #2c3e50;
            margin-bottom: 20px;
            position: relative;
            padding-bottom: 10px;
        }

        .concept-content h2::after {
            content: '';
            position: absolute;
            bottom: 0;
            left: 50%;
            transform: translateX(-50%);
            width: 60px;
            height: 3px;
            background: linear-gradient(90deg, #2c3e50, #34495e);
            border-radius: 2px;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(10px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .input-section {
            background: linear-gradient(145deg, #ffffff, #f8f8f8);
            border: 1px solid #eaeaea;
            padding: 25px;
            border-radius: 12px;
            margin-bottom: 40px;
        }

        .url-input-container,
        .file-input-container {
            margin-bottom: 25px;
        }

        .url-input-container h3,
        .file-input-container h3 {
            color: #2c3e50;
            margin-bottom: 15px;
            font-size: 1.2em;
        }

        .input-group {
            display: flex;
            gap: 10px;
            align-items: center;
        }

        .custom-input {
            flex: 1;
            padding: 12px 15px;
            border: 1px solid #e0e0e0;
            border-radius: 8px;
            font-size: 1em;
            transition: all 0.3s ease;
        }

        .custom-input:focus {
            outline: none;
            border-color: #2c3e50;
            box-shadow: 0 0 0 2px rgba(44, 62, 80, 0.1);
        }

        .submit-btn {
            background: linear-gradient(145deg, #2c3e50, #34495e);
            padding: 12px 25px;
            border-radius: 8px;
            color: white;
            border: none;
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .submit-btn:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.1);
        }

        .file-upload-label {
            background: linear-gradient(145deg, #2c3e50, #34495e);
            color: white;
            padding: 12px 25px;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.3s ease;
        }

        .file-upload-label:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.1);
        }

        .file-input {
            display: none;
        }

        .file-name {
            margin-left: 10px;
            color: #666;
        }

        .section-divider {
            text-align: center;
            position: relative;
            margin: 40px 0;
        }

        .section-divider::before {
            content: '';
            position: absolute;
            top: 50%;
            left: 0;
            right: 0;
            height: 1px;
            background: #e0e0e0;
        }

        .section-divider span {
            background: white;
            padding: 0 20px;
            color: #666;
            position: relative;
            font-size: 1.1em;
        }

        @media (max-width: 600px) {
            .input-group {
                flex-direction: column;
            }
            
            .submit-btn,
            .file-upload-label {
                width: 100%;
                text-align: center;
            }
            
            .file-name {
                margin: 10px 0 0 0;
                display: block;
            }
        }

        .topics-grid {
            display: flex;
            flex-direction: column;
            gap: 15px;
            padding: 20px 0;
        }

        .topic-card {
            background: linear-gradient(145deg, #ffffff, #f8f8f8);
            border: 1px solid #eaeaea;
            border-radius: 12px;
            padding: 20px 25px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            transition: all 0.3s ease;
            cursor: pointer;
        }

        .topic-card:hover {
            transform: translateX(5px);
            box-shadow: 0 4px 15px rgba(0,0,0,0.1);
            background: linear-gradient(145deg, #f8f8f8, #f0f0f0);
        }

        .topic-card-content {
            text-align: left;
        }

        .topic-card h3 {
            color: #2c3e50;
            margin-bottom: 8px;
            font-size: 1.2em;
        }

        .topic-card p {
            color: #666;
            font-size: 0.9em;
            line-height: 1.4;
            margin: 0;
        }

        .topic-card-arrow {
            color: #2c3e50;
            font-size: 1.5em;
            opacity: 0.6;
            transition: all 0.3s ease;
        }

        .topic-card:hover .topic-card-arrow {
            opacity: 1;
            transform: translateX(5px);
        }

        .nav-links {
            display: flex;
            gap: 20px;
            align-items: center;
        }

        .login-link {
            color: white;
            text-decoration: none;
            font-size: 1.1em;
            font-weight: 500;
            transition: opacity 0.3s ease;
            display: flex;
            align-items: center;
            gap: 5px;
            padding: 8px 15px;
            border: 1px solid rgba(255, 255, 255, 0.3);
            border-radius: 20px;
        }

        .login-link:hover {
            opacity: 0.8;
            background: rgba(255, 255, 255, 0.1);
        }

        .login-link i {
            font-size: 0.9em;
        }

        .login-form {
            max-width: 400px;
            margin: 0 auto;
            padding: 20px;
        }

        .form-group {
            margin-bottom: 20px;
        }

        .form-group label {
            display: block;
            margin-bottom: 8px;
            color: #2c3e50;
            font-weight: 500;
        }

        .form-group input {
            width: 100%;
            padding: 12px;
            border: 1px solid #e0e0e0;
            border-radius: 8px;
            font-size: 1em;
            transition: all 0.3s ease;
        }

        .form-group input:focus {
            outline: none;
            border-color: #2c3e50;
            box-shadow: 0 0 0 2px rgba(44, 62, 80, 0.1);
        }

        #context-input {
            width: 100%;
            padding: 10px;
            margin-top: 10px;
            border: 1px solid #ddd;
            border-radius: 4px;
            font-family: inherit;
            resize: vertical;
        }

        /* Filename Input Interface Styles */
        .filename-input-container {
            display: flex;
            align-items: center;
            justify-content: center;
            min-height: 80vh;
            padding: 20px;
        }

        .filename-input-box {
            background: white;
            border-radius: 12px;
            padding: 40px;
            box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
            border: 1px solid rgba(0, 0, 0, 0.1);
            text-align: center;
            max-width: 500px;
            width: 100%;
        }

        .filename-input-box h2 {
            color: var(--primary-color);
            margin-bottom: 16px;
            font-weight: 600;
            font-size: 2rem;
        }

        .filename-input-box p {
            color: var(--text-secondary);
            margin-bottom: 30px;
            font-size: 1.1rem;
            line-height: 1.5;
        }

        .input-group {
            display: flex;
            gap: 12px;
            margin-bottom: 20px;
        }

        .input-group input {
            flex: 1;
            padding: 14px 18px;
            border: 2px solid var(--border-color);
            border-radius: 8px;
            font-size: 1rem;
            font-family: 'Inter', sans-serif;
            transition: all 0.2s ease;
            background: var(--bg-secondary);
        }

        .input-group input:focus {
            outline: none;
            border-color: var(--primary-color);
            box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
        }

        .input-group button {
            padding: 14px 24px;
            background: var(--primary-color);
            color: white;
            border: none;
            border-radius: 8px;
            font-size: 1rem;
            font-weight: 500;
            cursor: pointer;
            transition: all 0.2s ease;
            font-family: 'Inter', sans-serif;
        }

        .input-group button:hover {
            background: var(--primary-dark);
            transform: translateY(-1px);
            box-shadow: 0 4px 12px rgba(79, 70, 229, 0.3);
        }

        .input-group button:active {
            transform: translateY(0);
        }

        /* Responsive design for filename input */
        @media (max-width: 600px) {
            .filename-input-box {
                padding: 30px 20px;
                margin: 20px;
            }
            
            .input-group {
                flex-direction: column;
            }
            
            .filename-input-box h2 {
                font-size: 1.5rem;
            }
        }

        /* Quiz Selection Grid Styles */
        .quiz-selection-container {
            max-width: 1200px;
            margin: 80px auto 40px;
            padding: 30px;
        }

        .selection-header {
            text-align: center;
            margin-bottom: 40px;
        }

        .selection-header h2 {
            font-size: 2.5em;
            color: white;
            margin-bottom: 10px;
            text-shadow: 0 2px 4px rgba(0,0,0,0.3);
        }

        .selection-header p {
            color: #d1e7dd;
            font-size: 1.1em;
            margin: 10px 0 0 0;
        }

        .quizzes-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
            gap: 25px;
            margin-top: 30px;
        }

        .quiz-card {
            background: rgba(255, 255, 255, 0.95);
            border-radius: 20px;
            padding: 25px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
            transition: all 0.3s ease;
            display: flex;
            flex-direction: column;
            min-height: 280px;
            position: relative;
            overflow: hidden;
        }

        .quiz-card:hover {
            transform: translateY(-8px);
            box-shadow: 0 15px 40px rgba(0, 0, 0, 0.3);
            background: rgba(255, 255, 255, 1);
        }

        .quiz-card-header {
            margin-bottom: 15px;
        }

        .quiz-card-header h3 {
            font-size: 1.4em;
            color: #2c3e50;
            margin: 0 0 10px 0;
            line-height: 1.3;
        }

        .quiz-card-meta {
            display: flex;
            gap: 10px;
            flex-wrap: wrap;
            margin-bottom: 10px;
        }

        .difficulty {
            padding: 4px 12px;
            border-radius: 15px;
            font-size: 0.8em;
            font-weight: 600;
            text-transform: uppercase;
            letter-spacing: 0.5px;
        }

        .difficulty-beginner {
            background: linear-gradient(145deg, #27ae60, #2ecc71);
            color: white;
        }

        .difficulty-intermediate {
            background: linear-gradient(145deg, #f39c12, #e67e22);
            color: white;
        }

        .difficulty-advanced {
            background: linear-gradient(145deg, #e74c3c, #c0392b);
            color: white;
        }

        .question-count {
            padding: 4px 12px;
            background: linear-gradient(145deg, #3498db, #2980b9);
            color: white;
            border-radius: 15px;
            font-size: 0.8em;
            font-weight: 500;
        }

        .quiz-card-description {
            color: #666;
            font-size: 0.95em;
            line-height: 1.5;
            margin-bottom: 15px;
            flex-grow: 1;
        }

        .quiz-card-tags {
            display: flex;
            flex-wrap: wrap;
            gap: 6px;
            margin-bottom: 20px;
        }

        .tag {
            background: linear-gradient(145deg, #ecf0f1, #bdc3c7);
            color: #2c3e50;
            padding: 3px 8px;
            border-radius: 10px;
            font-size: 0.75em;
            font-weight: 500;
        }

        .quiz-card-footer {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-top: auto;
            padding-top: 15px;
            border-top: 1px solid #eee;
        }

        .created-date {
            font-size: 0.8em;
            color: #888;
        }

        .start-quiz-btn {
            background: linear-gradient(145deg, #2c3e50, #34495e);
            color: white;
            border: none;
            padding: 10px 20px;
            border-radius: 25px;
            cursor: pointer;
            font-weight: 600;
            font-size: 0.9em;
            transition: all 0.3s ease;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .start-quiz-btn:hover {
            background: linear-gradient(145deg, #34495e, #2c3e50);
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.2);
        }

        .start-quiz-btn i {
            font-size: 0.8em;
            transition: transform 0.3s ease;
        }

        .start-quiz-btn:hover i {
            transform: translateX(3px);
        }

        /* Back Button Styles */
        .quiz-header {
            padding: 0 40px 20px;
            margin-top: 20px;
        }

        .back-btn {
            background: linear-gradient(145deg, #95a5a6, #7f8c8d);
            color: white;
            border: none;
            padding: 10px 20px;
            border-radius: 25px;
            cursor: pointer;
            font-weight: 600;
            font-size: 0.9em;
            transition: all 0.3s ease;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .back-btn:hover {
            background: linear-gradient(145deg, #7f8c8d, #95a5a6);
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.2);
        }

        .back-btn i {
            font-size: 0.8em;
            transition: transform 0.3s ease;
        }

        .back-btn:hover i {
            transform: translateX(-3px);
        }

        /* Responsive Grid */
        @media (max-width: 1200px) {
            .quizzes-grid {
                grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
                gap: 20px;
            }
        }

        @media (max-width: 768px) {
            .quiz-selection-container {
                padding: 20px 15px;
                margin: 60px auto 20px;
            }
            
            .selection-header h2 {
                font-size: 2em;
            }
            
            .quizzes-grid {
                grid-template-columns: 1fr;
                gap: 15px;
            }
            
            .quiz-card {
                padding: 20px;
                min-height: 250px;
            }
            
            .quiz-card-footer {
                flex-direction: column;
                gap: 10px;
                align-items: stretch;
            }
            
            .start-quiz-btn {
                width: 100%;
                justify-content: center;
            }
            
            .quiz-header {
                padding: 0 20px 15px;
            }
        }

        /* Quiz Generator Styles */
        .quiz-generator {
            background: rgba(255, 255, 255, 0.1);
            border-radius: 15px;
            padding: 25px;
            margin: 30px 0;
            border: 1px solid rgba(255, 255, 255, 0.2);
            backdrop-filter: blur(10px);
        }

        .quiz-generator h3 {
            color: #ffffff;
            font-size: 1.4em;
            margin: 0 0 20px 0;
            text-align: center;
            font-weight: 600;
        }

        .generator-input {
            display: flex;
            gap: 15px;
            align-items: center;
            max-width: 600px;
            margin: 0 auto;
        }

        #topic-input {
            flex: 1;
            padding: 15px 20px;
            border: 2px solid rgba(255, 255, 255, 0.3);
            border-radius: 25px;
            background: rgba(255, 255, 255, 0.9);
            font-size: 1.1em;
            color: #2c3e50;
            outline: none;
            transition: all 0.3s ease;
        }

        #topic-input:focus {
            border-color: #3498db;
            background: rgba(255, 255, 255, 1);
            box-shadow: 0 0 0 3px rgba(52, 152, 219, 0.2);
        }

        #topic-input::placeholder {
            color: #7f8c8d;
            font-style: italic;
        }

        #generate-quiz-btn {
            padding: 15px 25px;
            background: linear-gradient(145deg, #3498db, #2980b9);
            color: white;
            border: none;
            border-radius: 25px;
            font-size: 1.1em;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s ease;
            white-space: nowrap;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        #generate-quiz-btn:hover:not(:disabled) {
            background: linear-gradient(145deg, #2980b9, #3498db);
            transform: translateY(-2px);
            box-shadow: 0 6px 20px rgba(52, 152, 219, 0.3);
        }

        #generate-quiz-btn:disabled {
            background: linear-gradient(145deg, #95a5a6, #7f8c8d);
            cursor: not-allowed;
            transform: none;
            box-shadow: none;
        }

        .generation-status {
            text-align: center;
            margin-top: 15px;
            padding: 15px;
            background: rgba(52, 152, 219, 0.1);
            border: 1px solid rgba(52, 152, 219, 0.3);
            border-radius: 10px;
            color: #3498db;
            font-weight: 500;
        }

        .generation-status i {
            margin-right: 10px;
        }

        @media (max-width: 768px) {
            .generator-input {
                flex-direction: column;
                gap: 15px;
            }

            #topic-input {
                width: 100%;
            }

            #generate-quiz-btn {
                width: 100%;
                justify-content: center;
            }

            .quiz-generator {
                padding: 20px 15px;
                margin: 20px 0;
            }
        }