:root {
            --sage-light: #e8f5e9;
            --sage-medium: #c8e6c9;
            --beige: #f5f5dc;
            --off-white: #fafafa;
            --dark-green: #2e7d32;
            --dark-green-hover: #1b5e20;
            --amber: #ff8f00;
            --amber-light: #fff3e0;
            --red: #c62828;
            --red-light: #ffebee;
            --green: #2e7d32;
            --green-light: #e8f5e9;
            --text: #333;
            --text-light: #666;
            --border: #c8e6c9;
        }

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

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

        /* Header */
        header {
            background: var(--sage-light);
            border-bottom: 2px solid var(--border);
            padding: 1rem;
            position: sticky;
            top: 0;
            z-index: 100;
        }

        .header-content {
            max-width: 1200px;
            margin: 0 auto;
            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:hover {
            color: var(--dark-green-hover);
        }

        .exercise-indicator {
            background: var(--dark-green);
            color: white;
            padding: 0.5rem 1rem;
            border-radius: 20px;
            font-size: 0.9rem;
            font-weight: 500;
        }

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

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

        .nav-btn {
            padding: 0.75rem 1.5rem;
            border-radius: 8px;
            text-decoration: none;
            font-weight: 500;
            transition: all 0.3s;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }

        .nav-btn-prev {
            background: var(--beige);
            color: var(--text);
        }

        .nav-btn-prev:hover {
            background: #e8e8c8;
        }

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

        .nav-btn-next:hover {
            background: var(--dark-green-hover);
        }

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

        /* Progress Bar */
        .progress-container {
            background: white;
            padding: 1.5rem;
            border-radius: 12px;
            margin-bottom: 2rem;
            box-shadow: 0 2px 4px rgba(0,0,0,0.1);
        }

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

        .progress-title {
            font-size: 1.1rem;
            color: var(--dark-green);
            font-weight: 600;
        }

        .progress-percentage {
            font-weight: bold;
            color: var(--dark-green);
        }

        .progress-bar {
            width: 100%;
            height: 12px;
            background: var(--sage-light);
            border-radius: 6px;
            overflow: hidden;
        }

        .progress-fill {
            height: 100%;
            background: linear-gradient(90deg, var(--dark-green), var(--sage-medium));
            border-radius: 6px;
            transition: width 0.5s ease;
            width: 0%;
        }

        .progress-actions {
            display: flex;
            gap: 1rem;
            margin-top: 1rem;
            flex-wrap: wrap;
        }

        .checkbox-label {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            cursor: pointer;
            font-size: 0.9rem;
        }

        .checkbox-label input[type="checkbox"] {
            width: 18px;
            height: 18px;
            accent-color: var(--dark-green);
        }

        /* Section Styles */
        section {
            background: white;
            border-radius: 12px;
            padding: 2rem;
            margin-bottom: 2rem;
            box-shadow: 0 2px 8px rgba(0,0,0,0.05);
        }

        h1 {
            color: var(--dark-green);
            font-size: 2rem;
            margin-bottom: 0.5rem;
        }

        .subtitle {
            color: var(--text-light);
            font-size: 1.1rem;
            margin-bottom: 2rem;
        }

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

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

        p {
            margin-bottom: 1rem;
            line-height: 1.8;
        }

        .german-term {
            font-weight: 600;
            color: var(--dark-green);
        }

        .english-trans {
            color: var(--text-light);
            font-style: italic;
        }

        /* Toggle Button */
        .toggle-btn {
            background: var(--amber-light);
            color: var(--amber);
            border: 2px solid var(--amber);
            padding: 0.75rem 1.5rem;
            border-radius: 8px;
            cursor: pointer;
            font-weight: 600;
            margin: 1rem 0;
            transition: all 0.3s;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }

        .toggle-btn:hover {
            background: var(--amber);
            color: white;
        }

        .toggle-btn.active {
            background: var(--amber);
            color: white;
        }

        /* Comparison Table */
        .comparison-table {
            width: 100%;
            border-collapse: collapse;
            margin: 1.5rem 0;
            background: var(--off-white);
            border-radius: 8px;
            overflow: hidden;
        }

        .comparison-table th,
        .comparison-table td {
            padding: 1rem;
            text-align: left;
            border-bottom: 1px solid var(--border);
        }

        .comparison-table th {
            background: var(--sage-light);
            color: var(--dark-green);
            font-weight: 600;
        }

        .comparison-table tr:hover {
            background: var(--sage-light);
        }

        .comparison-table td {
            cursor: pointer;
            transition: all 0.2s;
            position: relative;
        }

        .comparison-table td:hover {
            background: var(--sage-medium);
        }

        .verb-form {
            font-weight: 600;
            font-size: 1.1rem;
        }

        .irregular {
            background: var(--amber-light) !important;
            color: var(--amber);
            font-weight: 700;
        }

        .irregular-highlight {
            background: var(--amber-light);
            color: var(--amber);
            padding: 0.2rem 0.4rem;
            border-radius: 4px;
            font-weight: 700;
        }

        .pronunciation-hint {
            font-size: 0.8rem;
            color: var(--text-light);
            margin-top: 0.25rem;
        }

        /* Example Box */
        .example-box {
            background: var(--sage-light);
            border-left: 4px solid var(--dark-green);
            padding: 1rem;
            margin: 1rem 0;
            border-radius: 0 8px 8px 0;
            display: none;
        }

        .example-box.active {
            display: block;
            animation: slideDown 0.3s ease;
        }

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

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

        .flashcard {
            background: var(--beige);
            border-radius: 8px;
            padding: 1.5rem;
            cursor: pointer;
            transition: all 0.3s;
            position: relative;
            min-height: 100px;
            display: flex;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            text-align: center;
            border: 2px solid transparent;
        }

        .flashcard:hover, .flashcard:focus {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.1);
            border-color: var(--dark-green);
            outline: none;
        }

        .flashcard .german {
            font-size: 1.2rem;
            font-weight: 600;
            color: var(--dark-green);
            display: none;
        }

        .flashcard .english {
            color: var(--text);
            font-size: 1rem;
        }

        .flashcard.revealed .german {
            display: block;
        }

        .flashcard.revealed .english {
            color: var(--text-light);
            font-size: 0.9rem;
            margin-top: 0.5rem;
        }

        .flashcard-hint {
            position: absolute;
            top: 0.5rem;
            right: 0.5rem;
            font-size: 0.7rem;
            color: var(--text-light);
            opacity: 0.7;
        }

        /* Exercise Styles */
        .exercise {
            background: var(--off-white);
            border-radius: 8px;
            padding: 1.5rem;
            margin: 1.5rem 0;
        }

        .exercise-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 1rem;
            flex-wrap: wrap;
            gap: 0.5rem;
        }

        .exercise-title {
            font-weight: 600;
            color: var(--dark-green);
            font-size: 1.1rem;
        }

        .exercise-number {
            background: var(--dark-green);
            color: white;
            width: 28px;
            height: 28px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 0.9rem;
            font-weight: 600;
        }

        .question {
            margin: 1rem 0;
            padding: 1rem;
            background: white;
            border-radius: 8px;
            border: 1px solid var(--border);
            transition: box-shadow 0.2s;
        }

        .question:focus-within {
            box-shadow: 0 0 0 3px rgba(46, 125, 50, 0.1);
            border-color: var(--dark-green);
        }

        .question-text {
            margin-bottom: 0.75rem;
            line-height: 1.6;
        }

        .input-row {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            flex-wrap: wrap;
        }

        .input-field {
            padding: 0.5rem 0.75rem;
            border: 2px solid var(--border);
            border-radius: 6px;
            font-size: 1rem;
            min-width: 120px;
            transition: all 0.3s;
        }

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

        .input-field.correct {
            border-color: var(--green);
            background: var(--green-light);
        }

        .input-field.incorrect {
            border-color: var(--red);
            background: var(--red-light);
        }

        .input-field.warning {
            border-color: var(--amber);
            background: var(--amber-light);
            animation: shake 0.5s;
        }

        @keyframes shake {
            0%, 100% { transform: translateX(0); }
            25% { transform: translateX(-5px); }
            75% { transform: translateX(5px); }
        }

        .dropdown {
            padding: 0.5rem 0.75rem;
            border: 2px solid var(--border);
            border-radius: 6px;
            font-size: 1rem;
            background: white;
            cursor: pointer;
            transition: all 0.2s;
        }

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

        .dropdown.correct {
            border-color: var(--green);
            background: var(--green-light);
        }

        .dropdown.incorrect {
            border-color: var(--red);
            background: var(--red-light);
        }

        .hint {
            font-size: 0.85rem;
            color: var(--text-light);
            margin-top: 0.5rem;
            font-style: italic;
        }

        .correction {
            display: none;
            color: var(--green);
            font-weight: 600;
            margin-top: 0.5rem;
            font-size: 0.9rem;
            padding: 0.5rem;
            background: var(--green-light);
            border-radius: 4px;
        }

        .correction.show {
            display: block;
            animation: fadeIn 0.3s;
        }

        @keyframes fadeIn {
            from { opacity: 0; }
            to { opacity: 1; }
        }

        /* Practice Mode */
        .practice-mode {
            background: linear-gradient(135deg, var(--sage-light), var(--beige));
            border-radius: 12px;
            padding: 2rem;
            text-align: center;
            margin: 2rem 0;
        }

        .practice-display {
            font-size: 2rem;
            color: var(--dark-green);
            font-weight: 700;
            margin: 1rem 0;
            min-height: 60px;
            display: flex;
            align-items: center;
            justify-content: center;
            flex-direction: column;
        }

        .practice-input {
            font-size: 1.2rem;
            padding: 0.75rem 1rem;
            border: 3px solid var(--dark-green);
            border-radius: 8px;
            text-align: center;
            width: 200px;
            margin: 1rem 0;
        }

        .practice-feedback {
            min-height: 30px;
            font-weight: 600;
            margin: 0.5rem 0;
        }

        .practice-feedback.correct {
            color: var(--green);
        }

        .practice-feedback.incorrect {
            color: var(--red);
        }

        .practice-stats {
            display: flex;
            justify-content: center;
            gap: 2rem;
            margin-top: 1rem;
            font-size: 0.9rem;
            color: var(--text-light);
        }

        /* Buttons */
        .btn-group {
            display: flex;
            gap: 1rem;
            margin: 2rem 0;
            flex-wrap: wrap;
        }

        .btn {
            padding: 0.875rem 1.75rem;
            border: none;
            border-radius: 8px;
            font-size: 1rem;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.3s;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
        }

        .btn:disabled {
            opacity: 0.5;
            cursor: not-allowed;
        }

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

        .btn-primary:hover:not(:disabled) {
            background: var(--dark-green-hover);
            transform: translateY(-1px);
            box-shadow: 0 4px 12px rgba(46, 125, 50, 0.3);
        }

        .btn-secondary {
            background: var(--beige);
            color: var(--text);
        }

        .btn-secondary:hover:not(:disabled) {
            background: #e8e8c8;
        }

        .btn-danger {
            background: var(--red-light);
            color: var(--red);
            border: 1px solid var(--red);
        }

        .btn-danger:hover:not(:disabled) {
            background: var(--red);
            color: white;
        }

        /* Memorization Mode */
        .memorization-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 1rem;
            margin: 1.5rem 0;
        }

        .memo-card {
            background: white;
            border: 2px solid var(--border);
            border-radius: 8px;
            padding: 1rem;
            text-align: center;
            transition: all 0.3s;
            cursor: pointer;
        }

        .memo-card:hover, .memo-card:focus {
            border-color: var(--dark-green);
            transform: translateY(-2px);
            box-shadow: 0 4px 8px rgba(0,0,0,0.1);
            outline: none;
        }

        .memo-card.hidden {
            background: var(--sage-light);
            border-style: dashed;
        }

        .memo-card.hidden .memo-content {
            visibility: hidden;
        }

        .memo-pronoun {
            font-size: 0.9rem;
            color: var(--text-light);
            margin-bottom: 0.5rem;
        }

        .memo-verb {
            font-size: 1.3rem;
            font-weight: 600;
            color: var(--dark-green);
        }

        /* Footer */
        footer {
            background: var(--sage-light);
            border-top: 2px solid var(--border);
            padding: 2rem 1rem;
            margin-top: 3rem;
        }

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

        .footer-links {
            display: flex;
            gap: 2rem;
            align-items: center;
        }

        .footer-links a {
            color: var(--dark-green);
            text-decoration: none;
            font-weight: 500;
        }

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

        /* Warning Toast */
        .toast {
            position: fixed;
            bottom: 2rem;
            left: 50%;
            transform: translateX(-50%) translateY(100px);
            background: var(--red);
            color: white;
            padding: 1rem 2rem;
            border-radius: 8px;
            box-shadow: 0 4px 12px rgba(0,0,0,0.2);
            opacity: 0;
            transition: all 0.3s;
            z-index: 1000;
            font-weight: 500;
            max-width: 90%;
            text-align: center;
        }

        .toast.show {
            transform: translateX(-50%) translateY(0);
            opacity: 1;
        }

        .toast.warning {
            background: var(--amber);
        }

        .toast.success {
            background: var(--green);
        }

        /* Status indicator */
        .status-indicator {
            display: inline-block;
            width: 8px;
            height: 8px;
            border-radius: 50%;
            margin-left: 0.5rem;
            background: #ccc;
        }

        .status-indicator.saved {
            background: var(--green);
        }

        .status-indicator.error {
            background: var(--red);
        }

        /* Responsive */
        @media (max-width: 768px) {
            h1 { font-size: 1.5rem; }
            h2 { font-size: 1.25rem; }
            
            .comparison-table {
                font-size: 0.9rem;
            }
            
            .comparison-table th,
            .comparison-table td {
                padding: 0.75rem 0.5rem;
            }

            .btn-group {
                flex-direction: column;
            }

            .btn {
                width: 100%;
                justify-content: center;
            }

            .footer-content {
                flex-direction: column;
                text-align: center;
            }

            .practice-stats {
                flex-direction: column;
                gap: 0.5rem;
            }
        }

        /* Accessibility */
        .sr-only {
            position: absolute;
            width: 1px;
            height: 1px;
            padding: 0;
            margin: -1px;
            overflow: hidden;
            clip: rect(0, 0, 0, 0);
            white-space: nowrap;
            border-width: 0;
        }

        :focus-visible {
            outline: 3px solid var(--amber);
            outline-offset: 2px;
        }

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

        /* Print styles */
        @media print {
            header, footer, .btn-group, .practice-mode, .nav-bar, .progress-actions {
                display: none;
            }
            
            section {
                box-shadow: none;
                page-break-inside: avoid;
            }

            .correction {
                display: block !important;
                color: #000;
                background: #f0f0f0;
            }
        }