:root {
            --sage-green: #e8f5e9;
            --warm-beige: #f5f5dc;
            --off-white: #fafafa;
            --dark-green: #2e7d32;
            --masculine-blue: #1976d2;
            --feminine-pink: #e91e63;
            --neuter-yellow: #fbc02d;
            --text-dark: #333;
            --text-light: #666;
            --border-color: #ddd;
            --shadow: 0 2px 8px rgba(0,0,0,0.1);
            --shadow-hover: 0 4px 16px rgba(0,0,0,0.15);
        }

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

        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
            background: var(--off-white);
            color: var(--text-dark);
            line-height: 1.6;
            font-size: 16px;
        }

        /* Header Styles */
        header {
            background: linear-gradient(135deg, var(--sage-green) 0%, var(--warm-beige) 100%);
            border-bottom: 3px solid var(--dark-green);
            padding: 1rem 0;
            position: sticky;
            top: 0;
            z-index: 100;
            box-shadow: var(--shadow);
        }

        .header-container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 1rem;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
            gap: 1rem;
        }

        .logo {
            font-size: 1.5rem;
            font-weight: bold;
            color: var(--dark-green);
            text-decoration: none;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .logo::before {
            content: "🌿";
        }

        .exercise-indicator {
            background: var(--dark-green);
            color: white;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            font-size: 0.9rem;
            font-weight: 600;
        }

        /* Navigation */
        .nav-bar {
            background: white;
            padding: 1rem 0;
            border-bottom: 1px solid var(--border-color);
        }

        .nav-container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 1rem;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .nav-btn {
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
            padding: 0.75rem 1.5rem;
            background: white;
            border: 2px solid var(--dark-green);
            color: var(--dark-green);
            text-decoration: none;
            border-radius: 8px;
            font-weight: 600;
            transition: all 0.3s ease;
        }

        .nav-btn:hover {
            background: var(--sage-green);
            transform: translateY(-2px);
            box-shadow: var(--shadow);
        }

        .nav-btn.disabled {
            opacity: 0.5;
            pointer-events: none;
            border-color: #ccc;
            color: #999;
        }

        /* Main Container */
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 2rem 1rem;
        }

        h1 {
            color: var(--dark-green);
            font-size: 2rem;
            margin-bottom: 1rem;
            text-align: center;
        }

        h2 {
            color: var(--dark-green);
            font-size: 1.5rem;
            margin: 2rem 0 1rem;
            border-bottom: 2px solid var(--sage-green);
            padding-bottom: 0.5rem;
        }

        h3 {
            color: var(--text-dark);
            font-size: 1.2rem;
            margin: 1.5rem 0 0.75rem;
        }

        /* Progress Bar */
        .progress-container {
            background: white;
            padding: 1rem;
            border-radius: 12px;
            margin-bottom: 2rem;
            box-shadow: var(--shadow);
            position: sticky;
            top: 80px;
            z-index: 99;
        }

        .progress-header {
            display: flex;
            justify-content: space-between;
            margin-bottom: 0.5rem;
            font-size: 0.9rem;
            color: var(--text-light);
        }

        .progress-bar {
            width: 100%;
            height: 8px;
            background: #e0e0e0;
            border-radius: 4px;
            overflow: hidden;
        }

        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, var(--dark-green), var(--masculine-blue));
            width: 0%;
            transition: width 0.3s ease;
        }

        /* Gender Color Legend */
        .gender-legend {
            display: flex;
            justify-content: center;
            gap: 1rem;
            margin: 2rem 0;
            flex-wrap: wrap;
        }

        .gender-badge {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            font-weight: 600;
            font-size: 0.9rem;
            box-shadow: var(--shadow);
        }

        .badge-masculine {
            background: rgba(25, 118, 210, 0.15);
            color: var(--masculine-blue);
            border: 2px solid var(--masculine-blue);
        }

        .badge-feminine {
            background: rgba(233, 30, 99, 0.15);
            color: var(--feminine-pink);
            border: 2px solid var(--feminine-pink);
        }

        .badge-neuter {
            background: rgba(251, 192, 45, 0.15);
            color: #f57f17;
            border: 2px solid var(--neuter-yellow);
        }

        /* Theory Cards */
        .theory-section {
            background: white;
            border-radius: 12px;
            padding: 2rem;
            margin-bottom: 2rem;
            box-shadow: var(--shadow);
        }

        .gender-card {
            border-left: 4px solid;
            padding: 1.5rem;
            margin: 1rem 0;
            background: var(--off-white);
            border-radius: 0 8px 8px 0;
        }

        .card-masculine {
            border-color: var(--masculine-blue);
            background: rgba(25, 118, 210, 0.05);
        }

        .card-feminine {
            border-color: var(--feminine-pink);
            background: rgba(233, 30, 99, 0.05);
        }

        .card-neuter {
            border-color: var(--neuter-yellow);
            background: rgba(251, 192, 45, 0.05);
        }

        .gender-title {
            font-size: 1.3rem;
            font-weight: bold;
            margin-bottom: 0.5rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .title-masculine { color: var(--masculine-blue); }
        .title-feminine { color: var(--feminine-pink); }
        .title-neuter { color: #f57f17; }

        .example-list {
            list-style: none;
            margin: 0.5rem 0;
        }

        .example-list li {
            padding: 0.25rem 0;
            padding-left: 1.5rem;
            position: relative;
        }

        .example-list li::before {
            content: "•";
            position: absolute;
            left: 0;
            font-weight: bold;
        }

        .card-masculine .example-list li::before { color: var(--masculine-blue); }
        .card-feminine .example-list li::before { color: var(--feminine-pink); }
        .card-neuter .example-list li::before { color: var(--neuter-yellow); }

        .german-term {
            font-weight: 600;
            font-size: 1.1rem;
        }

        .card-masculine .german-term { color: var(--masculine-blue); }
        .card-feminine .german-term { color: var(--feminine-pink); }
        .card-neuter .german-term { color: #f57f17; }

        .translation {
            color: var(--text-light);
            font-size: 0.95rem;
            font-style: italic;
        }

        /* Interactive Tables */
        .interactive-table {
            width: 100%;
            border-collapse: collapse;
            margin: 1rem 0;
            background: white;
            border-radius: 8px;
            overflow: hidden;
            box-shadow: var(--shadow);
        }

        .interactive-table th {
            background: var(--sage-green);
            color: var(--dark-green);
            padding: 1rem;
            text-align: left;
            font-weight: 600;
        }

        .interactive-table td {
            padding: 0.75rem 1rem;
            border-bottom: 1px solid var(--border-color);
        }

        .interactive-table tr:hover {
            background: var(--off-white);
        }

        .ending-cell {
            cursor: pointer;
            font-weight: 600;
            transition: all 0.2s;
            border-radius: 4px;
        }

        .ending-cell:hover {
            transform: scale(1.05);
            box-shadow: var(--shadow);
        }

        .ending-masculine { 
            background: rgba(25, 118, 210, 0.1); 
            color: var(--masculine-blue);
        }
        .ending-feminine { 
            background: rgba(233, 30, 99, 0.1); 
            color: var(--feminine-pink);
        }
        .ending-neuter { 
            background: rgba(251, 192, 45, 0.1); 
            color: #f57f17;
        }

        /* Exercise Containers */
        .exercise-container {
            background: white;
            border-radius: 12px;
            padding: 2rem;
            margin-bottom: 2rem;
            box-shadow: var(--shadow);
        }

        .exercise-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 1.5rem;
            flex-wrap: wrap;
            gap: 1rem;
        }

        .exercise-title {
            color: var(--dark-green);
            font-size: 1.3rem;
            margin: 0;
        }

        .exercise-number {
            background: var(--dark-green);
            color: white;
            width: 32px;
            height: 32px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: bold;
            flex-shrink: 0;
        }

        /* Form Elements */
        .question-group {
            margin: 1.5rem 0;
            padding: 1rem;
            background: var(--off-white);
            border-radius: 8px;
            border-left: 3px solid var(--dark-green);
        }

        .question-text {
            font-weight: 600;
            margin-bottom: 0.75rem;
            color: var(--text-dark);
        }

        .options-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 0.75rem;
        }

        .option-label {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            padding: 0.75rem;
            background: white;
            border: 2px solid var(--border-color);
            border-radius: 6px;
            cursor: pointer;
            transition: all 0.2s;
        }

        .option-label:hover {
            border-color: var(--dark-green);
            background: var(--sage-green);
        }

        .option-label input[type="radio"] {
            cursor: pointer;
        }

        .option-label.correct {
            background: rgba(46, 125, 50, 0.1);
            border-color: var(--dark-green);
            color: var(--dark-green);
        }

        .option-label.incorrect {
            background: rgba(211, 47, 47, 0.1);
            border-color: #d32f2f;
            color: #d32f2f;
        }

        .text-input {
            width: 100%;
            padding: 0.75rem;
            border: 2px solid var(--border-color);
            border-radius: 6px;
            font-size: 1rem;
            font-family: inherit;
            transition: border-color 0.2s;
        }

        .text-input:focus {
            outline: none;
            border-color: var(--dark-green);
            box-shadow: 0 0 0 3px rgba(46, 125, 50, 0.1);
        }

        .text-input.correct {
            border-color: var(--dark-green);
            background: rgba(46, 125, 50, 0.05);
        }

        .text-input.incorrect {
            border-color: #d32f2f;
            background: rgba(211, 47, 47, 0.05);
        }

        /* Grid for Exercise 8.2 */
        .noun-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
            gap: 1rem;
            margin: 1.5rem 0;
        }

        .noun-item {
            background: var(--off-white);
            padding: 1rem;
            border-radius: 8px;
            border: 2px solid var(--border-color);
        }

        .noun-word {
            font-size: 1.2rem;
            font-weight: 600;
            margin-bottom: 0.5rem;
            cursor: pointer;
            transition: color 0.2s;
        }

        .noun-word:hover {
            color: var(--dark-green);
        }

        .radio-group {
            display: flex;
            gap: 0.5rem;
            flex-wrap: wrap;
        }

        .gender-radio {
            display: flex;
            align-items: center;
            gap: 0.25rem;
            padding: 0.4rem 0.8rem;
            border-radius: 20px;
            cursor: pointer;
            font-size: 0.9rem;
            font-weight: 600;
            transition: all 0.2s;
            border: 2px solid transparent;
        }

        .gender-radio.m {
            background: rgba(25, 118, 210, 0.1);
            color: var(--masculine-blue);
        }
        .gender-radio.f {
            background: rgba(233, 30, 99, 0.1);
            color: var(--feminine-pink);
        }
        .gender-radio.nt {
            background: rgba(251, 192, 45, 0.1);
            color: #f57f17;
        }

        .gender-radio:hover {
            transform: translateY(-2px);
        }

        .gender-radio input {
            display: none;
        }

        .gender-radio.selected {
            border-width: 2px;
            border-style: solid;
        }

        .gender-radio.m.selected {
            border-color: var(--masculine-blue);
            background: rgba(25, 118, 210, 0.2);
        }
        .gender-radio.f.selected {
            border-color: var(--feminine-pink);
            background: rgba(233, 30, 99, 0.2);
        }
        .gender-radio.nt.selected {
            border-color: var(--neuter-yellow);
            background: rgba(251, 192, 45, 0.2);
        }

        /* Buttons */
        .btn-group {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
            margin-top: 2rem;
            justify-content: center;
        }

        .btn {
            padding: 0.75rem 1.5rem;
            border: none;
            border-radius: 8px;
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }

        .btn-primary {
            background: var(--dark-green);
            color: white;
        }

        .btn-primary:hover {
            background: #1b5e20;
            transform: translateY(-2px);
            box-shadow: var(--shadow-hover);
        }

        .btn-secondary {
            background: white;
            color: var(--dark-green);
            border: 2px solid var(--dark-green);
        }

        .btn-secondary:hover {
            background: var(--sage-green);
        }

        .btn-warning {
            background: #ff9800;
            color: white;
        }

        .btn-warning:hover {
            background: #f57c00;
        }

        /* Special Tools */
        .tool-box {
            background: linear-gradient(135deg, var(--sage-green), var(--warm-beige));
            border-radius: 12px;
            padding: 1.5rem;
            margin: 2rem 0;
            border: 2px solid var(--dark-green);
        }

        .tool-title {
            font-size: 1.2rem;
            color: var(--dark-green);
            margin-bottom: 1rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .compound-builder {
            display: flex;
            flex-wrap: wrap;
            gap: 0.5rem;
            align-items: center;
            justify-content: center;
            margin: 1rem 0;
        }

        .compound-part {
            padding: 0.5rem 1rem;
            background: white;
            border: 2px solid var(--border-color);
            border-radius: 6px;
            cursor: move;
            font-weight: 600;
            transition: all 0.2s;
        }

        .compound-part:hover {
            border-color: var(--dark-green);
            box-shadow: var(--shadow);
        }

        .compound-arrow {
            font-size: 1.5rem;
            color: var(--dark-green);
        }

        .compound-result {
            padding: 1rem;
            background: white;
            border-radius: 8px;
            text-align: center;
            font-size: 1.2rem;
            font-weight: 600;
            margin-top: 1rem;
            min-height: 50px;
            display: flex;
            align-items: center;
            justify-content: center;
        }

        /* Quiz Box */
        .quiz-container {
            background: white;
            border-radius: 12px;
            padding: 2rem;
            text-align: center;
            box-shadow: var(--shadow);
            margin: 2rem 0;
        }

        .quiz-word {
            font-size: 2rem;
            font-weight: bold;
            margin: 1rem 0;
            padding: 1rem;
            background: var(--off-white);
            border-radius: 8px;
        }

        .quiz-buttons {
            display: flex;
            justify-content: center;
            gap: 1rem;
            flex-wrap: wrap;
            margin: 1rem 0;
        }

        .quiz-btn {
            padding: 1rem 2rem;
            font-size: 1.2rem;
            font-weight: bold;
            border: 3px solid;
            border-radius: 8px;
            cursor: pointer;
            transition: all 0.2s;
            background: white;
        }

        .quiz-btn.m {
            border-color: var(--masculine-blue);
            color: var(--masculine-blue);
        }
        .quiz-btn.f {
            border-color: var(--feminine-pink);
            color: var(--feminine-pink);
        }
        .quiz-btn.nt {
            border-color: var(--neuter-yellow);
            color: #f57f17;
        }

        .quiz-btn:hover {
            transform: translateY(-3px);
            box-shadow: var(--shadow-hover);
        }

        .quiz-btn.correct {
            background: rgba(46, 125, 50, 0.2);
            border-color: var(--dark-green);
            color: var(--dark-green);
        }

        .quiz-btn.wrong {
            background: rgba(211, 47, 47, 0.2);
            border-color: #d32f2f;
            color: #d32f2f;
        }

        /* Exception Alert */
        .exception-alert {
            background: #fff3cd;
            border: 2px solid #ffc107;
            border-radius: 8px;
            padding: 1rem;
            margin: 1rem 0;
            display: flex;
            align-items: center;
            gap: 0.75rem;
        }

        .exception-alert::before {
            content: "⚠️";
            font-size: 1.5rem;
        }

        /* Mnemonic Cards */
        .mnemonic-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 1rem;
            margin: 1.5rem 0;
        }

        .mnemonic-card {
            background: white;
            border-radius: 12px;
            padding: 1.5rem;
            text-align: center;
            box-shadow: var(--shadow);
            transition: transform 0.2s;
        }

        .mnemonic-card:hover {
            transform: translateY(-5px);
            box-shadow: var(--shadow-hover);
        }

        .mnemonic-icon {
            font-size: 3rem;
            margin-bottom: 0.5rem;
        }

        .mnemonic-text {
            font-size: 1.1rem;
            color: var(--text-dark);
            font-weight: 600;
        }

        /* Feedback Message */
        .feedback {
            padding: 1rem;
            border-radius: 8px;
            margin: 1rem 0;
            display: none;
            align-items: center;
            gap: 0.5rem;
        }

        .feedback.show {
            display: flex;
        }

        .feedback.success {
            background: rgba(46, 125, 50, 0.1);
            color: var(--dark-green);
            border: 1px solid var(--dark-green);
        }

        .feedback.error {
            background: rgba(211, 47, 47, 0.1);
            color: #d32f2f;
            border: 1px solid #d32f2f;
        }

        /* Footer */
        footer {
            background: var(--sage-green);
            border-top: 3px solid var(--dark-green);
            padding: 2rem 0;
            margin-top: 3rem;
        }

        .footer-container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 1rem;
            text-align: center;
        }

        .footer-links {
            display: flex;
            justify-content: center;
            gap: 2rem;
            margin-bottom: 1rem;
            flex-wrap: wrap;
        }

        .footer-links a {
            color: var(--dark-green);
            text-decoration: none;
            font-weight: 600;
        }

        .footer-links a:hover {
            text-decoration: underline;
        }

        /* Responsive */
        @media (max-width: 768px) {
            h1 { font-size: 1.5rem; }
            h2 { font-size: 1.2rem; }
            
            .container {
                padding: 1rem;
            }
            
            .theory-section, .exercise-container {
                padding: 1rem;
            }
            
            .noun-grid {
                grid-template-columns: 1fr;
            }
            
            .quiz-word {
                font-size: 1.5rem;
            }
        }

        /* Utility Classes */
        .hidden { display: none !important; }
        .text-center { text-align: center; }
        .mb-1 { margin-bottom: 0.5rem; }
        .mb-2 { margin-bottom: 1rem; }
        .mt-2 { margin-top: 1rem; }
        
        .highlight-m { background: rgba(25, 118, 210, 0.2); padding: 2px 4px; border-radius: 3px; }
        .highlight-f { background: rgba(233, 30, 99, 0.2); padding: 2px 4px; border-radius: 3px; }
        .highlight-nt { background: rgba(251, 192, 45, 0.2); padding: 2px 4px; border-radius: 3px; }

        /* Smooth scroll */
        html {
            scroll-behavior: smooth;
        }

        /* Focus styles for accessibility */
        *:focus {
            outline: 2px solid var(--dark-green);
            outline-offset: 2px;
        }

        button:focus, a:focus, input:focus, select:focus {
            outline: 2px solid var(--dark-green);
            outline-offset: 2px;
        }