:root {
            --sage-light: #e8f5e9;
            --sage-medium: #c8e6c9;
            --sage-dark: #81c784;
            --beige: #f5f5dc;
            --beige-dark: #e8e4c9;
            --off-white: #fafafa;
            --green-primary: #2e7d32;
            --green-dark: #1b5e20;
            --green-light: #4caf50;
            --accent-warm: #ff7043;
            --text-primary: #2c3e2d;
            --text-secondary: #5a6b5c;
            --shadow: rgba(46, 125, 50, 0.1);
            --error: #e53935;
            --success: #43a047;
        }

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

        body {
            font-family: Georgia, 'Times New Roman', serif;
            background: linear-gradient(135deg, var(--off-white) 0%, var(--sage-light) 100%);
            color: var(--text-primary);
            line-height: 1.6;
            min-height: 100vh;
        }

        /* Header Styles */
        header {
            background: linear-gradient(135deg, var(--green-primary) 0%, var(--green-dark) 100%);
            color: white;
            padding: 1rem;
            position: sticky;
            top: 0;
            z-index: 1000;
            box-shadow: 0 2px 10px rgba(0,0,0,0.1);
        }

        .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;
            text-decoration: none;
            color: white;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .logo:hover {
            opacity: 0.9;
        }

        .exercise-indicator {
            background: rgba(255,255,255,0.2);
            padding: 0.5rem 1rem;
            border-radius: 20px;
            font-size: 0.9rem;
        }

        /* Navigation */
        .nav-buttons {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
        }

        .btn {
            padding: 0.75rem 1.5rem;
            border: none;
            border-radius: 8px;
            cursor: pointer;
            font-size: 1rem;
            transition: all 0.3s ease;
            text-decoration: none;
            display: inline-flex;
            align-items: center;
            gap: 0.5rem;
            font-family: inherit;
        }

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

        .btn-primary:hover {
            background: var(--green-dark);
            transform: translateY(-2px);
            box-shadow: 0 4px 12px var(--shadow);
        }

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

        .btn-secondary:hover {
            background: var(--beige-dark);
        }

        .btn-accent {
            background: var(--accent-warm);
            color: white;
        }

        .btn-accent:hover {
            background: #f4511e;
        }

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

        /* Progress Bar */
        .progress-container {
            background: var(--beige);
            border-radius: 10px;
            padding: 1rem;
            margin-bottom: 2rem;
            box-shadow: 0 2px 8px var(--shadow);
        }

        .progress-header {
            display: flex;
            justify-content: space-between;
            margin-bottom: 0.5rem;
            font-weight: bold;
            color: var(--green-dark);
        }

        .progress-bar {
            background: #ddd;
            border-radius: 10px;
            height: 20px;
            overflow: hidden;
        }

        .progress-fill {
            background: linear-gradient(90deg, var(--sage-dark), var(--green-primary));
            height: 100%;
            width: 0%;
            transition: width 0.5s ease;
            border-radius: 10px;
        }

        .completion-checkbox {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            margin-top: 0.5rem;
            cursor: pointer;
        }

        .completion-checkbox input {
            width: 20px;
            height: 20px;
            cursor: pointer;
        }

        /* Section Styles */
        .section {
            background: white;
            border-radius: 12px;
            padding: 2rem;
            margin-bottom: 2rem;
            box-shadow: 0 4px 20px var(--shadow);
            border-left: 5px solid var(--green-primary);
        }

        .section-title {
            color: var(--green-dark);
            font-size: 1.8rem;
            margin-bottom: 1.5rem;
            padding-bottom: 0.5rem;
            border-bottom: 2px solid var(--sage-medium);
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        /* Collapsible Theory Sections */
        .theory-item {
            margin-bottom: 1rem;
            border: 1px solid var(--sage-medium);
            border-radius: 8px;
            overflow: hidden;
        }

        .theory-header {
            background: var(--sage-light);
            padding: 1rem;
            cursor: pointer;
            display: flex;
            justify-content: space-between;
            align-items: center;
            transition: background 0.3s;
        }

        .theory-header:hover {
            background: var(--sage-medium);
        }

        .theory-header h3 {
            color: var(--green-dark);
            font-size: 1.2rem;
        }

        .toggle-icon {
            font-size: 1.5rem;
            transition: transform 0.3s;
        }

        .theory-item.collapsed .toggle-icon {
            transform: rotate(-90deg);
        }

        .theory-content {
            padding: 1.5rem;
            background: var(--off-white);
            display: none;
        }

        .theory-item.expanded .theory-content {
            display: block;
        }

        /* Reference Tables */
        .ref-table {
            width: 100%;
            border-collapse: collapse;
            margin: 1rem 0;
            background: white;
            border-radius: 8px;
            overflow: hidden;
            box-shadow: 0 2px 8px var(--shadow);
        }

        .ref-table th {
            background: var(--green-primary);
            color: white;
            padding: 1rem;
            text-align: left;
        }

        .ref-table td {
            padding: 0.75rem 1rem;
            border-bottom: 1px solid var(--sage-light);
        }

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

        .ref-table .example {
            color: var(--green-primary);
            font-weight: bold;
        }

        /* Interactive Elements */
        .german-term {
            position: relative;
            display: inline-block;
            color: var(--green-primary);
            font-weight: bold;
            cursor: help;
            border-bottom: 2px dotted var(--sage-dark);
        }

        .german-term:hover::after {
            content: attr(data-translation);
            position: absolute;
            bottom: 100%;
            left: 50%;
            transform: translateX(-50%);
            background: var(--green-dark);
            color: white;
            padding: 0.5rem 1rem;
            border-radius: 6px;
            white-space: nowrap;
            font-size: 0.9rem;
            font-weight: normal;
            z-index: 100;
            box-shadow: 0 4px 12px rgba(0,0,0,0.2);
        }

        .vowel-change {
            background: linear-gradient(120deg, #ffe082 0%, #ffe082 100%);
            background-repeat: no-repeat;
            background-size: 100% 40%;
            background-position: 0 88%;
            cursor: pointer;
            transition: all 0.3s;
        }

        .vowel-change:hover {
            background-size: 100% 100%;
        }

        .phonetic {
            color: var(--text-secondary);
            font-size: 0.9em;
            font-style: italic;
        }

        /* Exercise Styles */
        .exercise-container {
            margin-bottom: 2rem;
        }

        .exercise-title {
            color: var(--green-dark);
            font-size: 1.3rem;
            margin-bottom: 1rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .exercise-instruction {
            background: var(--beige);
            padding: 1rem;
            border-radius: 8px;
            margin-bottom: 1.5rem;
            border-left: 4px solid var(--accent-warm);
        }

        /* Conjugation Table Input */
        .conj-table {
            width: 100%;
            border-collapse: collapse;
            margin: 1rem 0;
        }

        .conj-table th, .conj-table td {
            padding: 0.75rem;
            text-align: center;
            border: 1px solid var(--sage-medium);
        }

        .conj-table th {
            background: var(--green-primary);
            color: white;
        }

        .conj-table td:first-child {
            background: var(--sage-light);
            font-weight: bold;
            color: var(--green-dark);
        }

        .conj-input {
            width: 100%;
            padding: 0.5rem;
            border: 2px solid var(--sage-medium);
            border-radius: 4px;
            font-size: 1rem;
            text-align: center;
            transition: all 0.3s;
        }

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

        .conj-input.correct {
            border-color: var(--success);
            background: #e8f5e9;
        }

        .conj-input.incorrect {
            border-color: var(--error);
            background: #ffebee;
        }

        .correct-answer {
            display: none;
            color: var(--success);
            font-size: 0.9rem;
            margin-top: 0.25rem;
        }

        .show-answers .correct-answer {
            display: block;
        }

        /* Toggle Buttons for Exercise 3.2 */
        .toggle-group {
            display: flex;
            gap: 0.5rem;
            justify-content: center;
        }

        .toggle-btn {
            padding: 0.5rem 1rem;
            border: 2px solid var(--sage-medium);
            background: white;
            border-radius: 20px;
            cursor: pointer;
            transition: all 0.3s;
            font-size: 1.2rem;
        }

        .toggle-btn:hover {
            border-color: var(--green-primary);
        }

        .toggle-btn.selected-tick {
            background: var(--success);
            color: white;
            border-color: var(--success);
        }

        .toggle-btn.selected-cross {
            background: var(--error);
            color: white;
            border-color: var(--error);
        }

        /* Text Input Exercise */
        .text-input-exercise {
            margin-bottom: 1.5rem;
        }

        .input-row {
            display: flex;
            gap: 1rem;
            align-items: center;
            margin-bottom: 0.5rem;
            flex-wrap: wrap;
        }

        .input-label {
            min-width: 200px;
            color: var(--text-secondary);
        }

        .text-input {
            flex: 1;
            min-width: 250px;
            padding: 0.75rem;
            border: 2px solid var(--sage-medium);
            border-radius: 6px;
            font-size: 1rem;
            transition: all 0.3s;
        }

        .text-input:focus {
            outline: none;
            border-color: var(--green-primary);
        }

        .text-input.correct {
            border-color: var(--success);
            background: #e8f5e9;
        }

        .text-input.incorrect {
            border-color: var(--error);
            background: #ffebee;
        }

        /* Mini Tool */
        .mini-tool {
            background: linear-gradient(135deg, var(--beige) 0%, var(--sage-light) 100%);
            padding: 2rem;
            border-radius: 12px;
            margin: 2rem 0;
            border: 2px dashed var(--green-primary);
        }

        .mini-tool h3 {
            color: var(--green-dark);
            margin-bottom: 1rem;
        }

        .tool-input-group {
            display: flex;
            gap: 1rem;
            margin-bottom: 1rem;
            flex-wrap: wrap;
        }

        .tool-input {
            flex: 1;
            min-width: 200px;
            padding: 0.75rem;
            border: 2px solid var(--green-primary);
            border-radius: 6px;
            font-size: 1rem;
        }

        .tool-result {
            background: white;
            padding: 1.5rem;
            border-radius: 8px;
            min-height: 100px;
            display: none;
        }

        .tool-result.show {
            display: block;
        }

        .conjugation-result {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
            gap: 0.5rem;
            margin-top: 1rem;
        }

        .conj-item {
            background: var(--sage-light);
            padding: 0.5rem;
            border-radius: 4px;
            text-align: center;
        }

        .conj-item.highlight {
            background: #fff3e0;
            border: 2px solid var(--accent-warm);
        }

        /* Action Buttons */
        .action-buttons {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
            margin: 2rem 0;
            justify-content: center;
        }

        /* Checklist */
        .checklist {
            background: var(--sage-light);
            padding: 1.5rem;
            border-radius: 8px;
            margin-top: 2rem;
        }

        .checklist h3 {
            color: var(--green-dark);
            margin-bottom: 1rem;
        }

        .checklist ul {
            list-style: none;
            padding-left: 0;
        }

        .checklist li {
            padding: 0.5rem 0;
            padding-left: 1.5rem;
            position: relative;
        }

        .checklist li::before {
            content: "✓";
            position: absolute;
            left: 0;
            color: var(--green-primary);
            font-weight: bold;
        }

        /* Footer */
        footer {
            background: var(--green-dark);
            color: white;
            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;
            flex-wrap: wrap;
        }

        .footer-links a {
            color: var(--sage-light);
            text-decoration: none;
            transition: color 0.3s;
        }

        .footer-links a:hover {
            color: white;
        }

        /* Responsive */
        @media (max-width: 768px) {
            .header-content {
                flex-direction: column;
                text-align: center;
            }

            .nav-buttons {
                justify-content: center;
            }

            .section {
                padding: 1rem;
            }

            .conj-table {
                font-size: 0.9rem;
            }

            .conj-table th, .conj-table td {
                padding: 0.5rem;
            }

            .input-row {
                flex-direction: column;
                align-items: stretch;
            }

            .input-label {
                min-width: auto;
            }
        }

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

        /* Focus Visible */
        *:focus-visible {
            outline: 3px solid var(--accent-warm);
            outline-offset: 2px;
        }

        /* Print Styles */
        @media print {
            header, footer, .action-buttons, .mini-tool {
                display: none;
            }

            .section {
                break-inside: avoid;
                box-shadow: none;
                border: 1px solid #ddd;
            }
        }

        /* Loading Animation */
        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(20px); }
            to { opacity: 1; transform: translateY(0); }
        }

        .section {
            animation: fadeIn 0.6s ease-out;
        }

        /* Tooltip for vowel patterns */
        .pattern-tooltip {
            position: fixed;
            background: var(--green-dark);
            color: white;
            padding: 1rem;
            border-radius: 8px;
            max-width: 300px;
            z-index: 1000;
            box-shadow: 0 4px 12px rgba(0,0,0,0.3);
            display: none;
        }

        .pattern-tooltip.show {
            display: block;
        }

        .pattern-tooltip h4 {
            margin-bottom: 0.5rem;
            color: var(--sage-light);
        }

        .pattern-tooltip ul {
            margin: 0;
            padding-left: 1.2rem;
        }

        .pattern-tooltip li {
            margin: 0.25rem 0;
        }