:root {
            --primary: #2563eb;
            --primary-dark: #1d4ed8;
            --medical: #059669;
            --medical-dark: #047857;
            --danger: #dc2626;
            --warning: #d97706;
            --bg: #f8fafc;
            --card: #ffffff;
            --text: #1e293b;
            --text-light: #64748b;
            --border: #e2e8f0;
            --shadow: 0 4px 6px -1px rgba(0,0,0,0.1);
        }

        [data-theme="dark"] {
            --primary: #3b82f6;
            --primary-dark: #2563eb;
            --medical: #10b981;
            --medical-dark: #059669;
            --bg: #0f172a;
            --card: #1e293b;
            --text: #f1f5f9;
            --text-light: #94a3b8;
            --border: #334155;
            --shadow: 0 4px 6px -1px rgba(0,0,0,0.3);
        }

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

        body {
            font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
            background: var(--bg);
            color: var(--text);
            line-height: 1.6;
            transition: background 0.3s, color 0.3s;
        }

        header {
            background: linear-gradient(135deg, var(--primary) 0%, var(--primary-dark) 100%);
            color: white;
            padding: 2rem 1rem;
            text-align: center;
            box-shadow: var(--shadow);
            position: relative;
        }

        h1 {
            font-size: 1.8rem;
            margin-bottom: 0.5rem;
        }

        .subtitle {
            opacity: 0.9;
            font-size: 1rem;
        }

        .exam-badge {
            display: inline-block;
            background: rgba(255,255,255,0.2);
            padding: 0.25rem 0.75rem;
            border-radius: 20px;
            font-size: 0.875rem;
            margin-top: 0.5rem;
        }

        .theme-toggle {
            position: absolute;
            top: 1rem;
            right: 1rem;
            background: rgba(255,255,255,0.2);
            border: none;
            color: white;
            padding: 0.5rem;
            border-radius: 50%;
            cursor: pointer;
            font-size: 1.25rem;
            transition: all 0.3s;
        }

        .theme-toggle:hover {
            background: rgba(255,255,255,0.3);
            transform: scale(1.1);
        }

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

        .stats-bar {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
            gap: 1rem;
            margin-bottom: 2rem;
        }

        .stat-card {
            background: var(--card);
            padding: 1rem;
            border-radius: 12px;
            box-shadow: var(--shadow);
            text-align: center;
            border-left: 4px solid var(--primary);
        }

        .stat-number {
            font-size: 2rem;
            font-weight: bold;
            color: var(--primary);
        }

        .stat-label {
            font-size: 0.875rem;
            color: var(--text-light);
        }

        .controls {
            display: flex;
            gap: 1rem;
            margin-bottom: 2rem;
            flex-wrap: wrap;
        }

        .search-box {
            flex: 1;
            min-width: 250px;
            position: relative;
        }

        .search-box input {
            width: 100%;
            padding: 0.75rem 1rem 0.75rem 2.5rem;
            border: 2px solid var(--border);
            border-radius: 8px;
            font-size: 1rem;
            transition: all 0.3s;
            background: var(--card);
            color: var(--text);
        }

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

        .search-box::before {
            content: "🔍";
            position: absolute;
            left: 0.75rem;
            top: 50%;
            transform: translateY(-50%);
        }

        .filter-tabs {
            display: flex;
            gap: 0.5rem;
            flex-wrap: wrap;
        }

        .tab {
            padding: 0.5rem 1rem;
            border: 2px solid var(--border);
            background: var(--card);
            border-radius: 8px;
            cursor: pointer;
            font-weight: 500;
            transition: all 0.3s;
            color: var(--text);
        }

        .tab:hover {
            border-color: var(--primary);
            color: var(--primary);
        }

        .tab.active {
            background: var(--primary);
            color: white;
            border-color: var(--primary);
        }

        .tab.medical {
            border-color: var(--medical);
            color: var(--medical);
        }

        .tab.medical.active {
            background: var(--medical);
            color: white;
        }

        .tab.unmastered {
            border-color: var(--warning);
            color: var(--warning);
        }

        .tab.unmastered.active {
            background: var(--warning);
            color: white;
        }

        .section-title {
            font-size: 1.5rem;
            margin: 2rem 0 1rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }

        .medical-tag {
            background: var(--medical);
            color: white;
            padding: 0.25rem 0.5rem;
            border-radius: 4px;
            font-size: 0.75rem;
            font-weight: bold;
        }

        .verbs-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
            gap: 1rem;
            margin-bottom: 3rem;
        }

        .verb-card {
            background: var(--card);
            border-radius: 12px;
            padding: 1.5rem;
            box-shadow: var(--shadow);
            border: 2px solid transparent;
            transition: all 0.3s;
            cursor: pointer;
            position: relative;
            overflow: hidden;
        }

        .verb-card:hover {
            transform: translateY(-2px);
            box-shadow: 0 10px 15px -3px rgba(0,0,0,0.1);
            border-color: var(--primary);
        }

        .verb-card.medical {
            border-left: 4px solid var(--medical);
        }

        .verb-card.mastered {
            background: linear-gradient(135deg, #ecfdf5 0%, #d1fae5 100%);
            border-color: var(--medical);
        }

        [data-theme="dark"] .verb-card.mastered {
            background: linear-gradient(135deg, #064e3b 0%, #065f46 100%);
        }

        .verb-card.mastered::after {
            content: "✓ Mastered";
            position: absolute;
            top: 0.5rem;
            right: 0.5rem;
            background: var(--medical);
            color: white;
            padding: 0.25rem 0.5rem;
            border-radius: 4px;
            font-size: 0.75rem;
        }

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

        .verb-infinitive {
            font-size: 1.25rem;
            font-weight: bold;
            color: var(--primary);
            font-family: 'Courier New', monospace;
        }

        .verb-card.medical .verb-infinitive {
            color: var(--medical);
        }

        .prefix-tag {
            background: #dbeafe;
            color: var(--primary);
            padding: 0.25rem 0.5rem;
            border-radius: 4px;
            font-size: 0.875rem;
            font-weight: bold;
        }

        [data-theme="dark"] .prefix-tag {
            background: #1e3a5f;
        }

        .verb-meaning {
            color: var(--text-light);
            margin-bottom: 0.5rem;
            font-size: 0.95rem;
        }

        .verb-example {
            background: var(--bg);
            padding: 0.75rem;
            border-radius: 8px;
            font-size: 0.9rem;
            border-left: 3px solid var(--border);
            margin-top: 0.5rem;
        }

        .verb-example .german {
            color: var(--text);
            font-weight: 500;
            margin-bottom: 0.25rem;
        }

        .verb-example .english {
            color: var(--text-light);
            font-size: 0.85rem;
        }

        .verb-example .highlight {
            color: var(--primary);
            font-weight: bold;
        }

        .verb-card.medical .verb-example .highlight {
            color: var(--medical);
        }

        .action-buttons {
            display: flex;
            gap: 0.5rem;
            margin-top: 1rem;
        }

        .btn {
            padding: 0.5rem 1rem;
            border: none;
            border-radius: 6px;
            cursor: pointer;
            font-size: 0.875rem;
            font-weight: 500;
            transition: all 0.3s;
            flex: 1;
        }

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

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

        .btn-success {
            background: var(--medical);
            color: white;
        }

        .btn-success:hover {
            background: var(--medical-dark);
        }

        .btn-outline {
            background: transparent;
            border: 2px solid var(--border);
            color: var(--text);
        }

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

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

        .btn-danger:hover {
            background: #b91c1c;
        }

        /* Quiz Mode Styles */
        .quiz-container {
            background: var(--card);
            border-radius: 16px;
            padding: 2rem;
            box-shadow: var(--shadow);
            margin-bottom: 2rem;
            display: none;
        }

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

        .quiz-question {
            font-size: 1.25rem;
            margin-bottom: 1.5rem;
            text-align: center;
        }

        .quiz-options {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
            gap: 1rem;
            margin-bottom: 1.5rem;
        }

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

        .quiz-option:hover {
            border-color: var(--primary);
            background: #eff6ff;
        }

        [data-theme="dark"] .quiz-option:hover {
            background: #1e293b;
        }

        .quiz-option.correct {
            background: #d1fae5;
            border-color: var(--medical);
            color: var(--medical-dark);
        }

        .quiz-option.wrong {
            background: #fee2e2;
            border-color: var(--danger);
            color: var(--danger);
        }

        .quiz-progress {
            height: 8px;
            background: var(--border);
            border-radius: 4px;
            overflow: hidden;
            margin-bottom: 1rem;
        }

        .quiz-progress-bar {
            height: 100%;
            background: var(--primary);
            transition: width 0.3s;
        }

        /* Study Mode Toggle */
        .mode-toggle {
            display: flex;
            gap: 1rem;
            margin-bottom: 2rem;
            background: var(--card);
            padding: 0.5rem;
            border-radius: 12px;
            box-shadow: var(--shadow);
            width: fit-content;
        }

        .mode-btn {
            padding: 0.75rem 1.5rem;
            border: none;
            background: transparent;
            border-radius: 8px;
            cursor: pointer;
            font-weight: 500;
            transition: all 0.3s;
            color: var(--text);
        }

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

        .hidden {
            display: none !important;
        }

        /* Responsive */
        @media (max-width: 768px) {
            .verbs-grid {
                grid-template-columns: 1fr;
            }
            
            h1 {
                font-size: 1.5rem;
            }

            .mode-toggle {
                flex-wrap: wrap;
                width: 100%;
            }

            .mode-btn {
                flex: 1;
                min-width: 120px;
            }
        }

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

        .verb-card {
            animation: fadeIn 0.3s ease;
        }

        .stats-overview {
            background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
            color: white;
            padding: 1.5rem;
            border-radius: 12px;
            margin-bottom: 2rem;
        }

        .stats-grid {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 1rem;
            text-align: center;
        }

        .stat-item h3 {
            font-size: 2rem;
            margin-bottom: 0.25rem;
        }

        .stat-item p {
            opacity: 0.9;
            font-size: 0.875rem;
        }

        .streak-display {
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 0.5rem;
            margin-top: 0.5rem;
            font-size: 0.9rem;
        }

        .streak-fire {
            font-size: 1.2rem;
        }

        .reset-btn {
            background: transparent;
            border: 1px solid rgba(255,255,255,0.3);
            color: white;
            padding: 0.25rem 0.75rem;
            border-radius: 4px;
            cursor: pointer;
            font-size: 0.8rem;
            margin-top: 0.5rem;
            transition: all 0.3s;
        }

        .reset-btn:hover {
            background: rgba(255,255,255,0.2);
        }

        .difficulty-badge {
            position: absolute;
            top: 0.5rem;
            left: 0.5rem;
            padding: 0.2rem 0.4rem;
            border-radius: 4px;
            font-size: 0.7rem;
            font-weight: bold;
        }

        .difficulty-b1 {
            background: #3b82f6;
            color: white;
        }

        .difficulty-c1 {
            background: #8b5cf6;
            color: white;
        }

        .conjugation-modal {
            display: none;
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            background: rgba(0,0,0,0.5);
            z-index: 1000;
            justify-content: center;
            align-items: center;
        }

        .conjugation-modal.active {
            display: flex;
        }

        .conjugation-content {
            background: var(--card);
            padding: 2rem;
            border-radius: 16px;
            max-width: 500px;
            width: 90%;
            max-height: 80vh;
            overflow-y: auto;
        }

        .conjugation-table {
            width: 100%;
            border-collapse: collapse;
            margin-top: 1rem;
        }

        .conjugation-table th,
        .conjugation-table td {
            padding: 0.75rem;
            text-align: left;
            border-bottom: 1px solid var(--border);
        }

        .conjugation-table th {
            background: var(--bg);
            font-weight: 600;
        }

        .close-modal {
            float: right;
            font-size: 1.5rem;
            cursor: pointer;
            color: var(--text-light);
        }

        .close-modal:hover {
            color: var(--text);
        }

        .toast {
            position: fixed;
            bottom: 2rem;
            right: 2rem;
            background: var(--medical);
            color: white;
            padding: 1rem 1.5rem;
            border-radius: 8px;
            box-shadow: var(--shadow);
            transform: translateX(150%);
            transition: transform 0.3s;
            z-index: 1001;
        }

        .toast.show {
            transform: translateX(0);
        }