:root {
            /* Design System */
            --bg-body: #F8FAFC;
            --bg-surface: #FFFFFF;
            --text-main: #0F172A;
            --text-sub: #64748B;
            --border: #E2E8F0;

            /* Theme Color (中1: Blue) */
            --theme-color: #3B82F6;
            --theme-light: #EFF6FF;
            --theme-dark: #2563EB;
            --radius: 16px;

            /* Feedback Colors */
            --success-bg: #ECFDF5;
            --success-border: #10B981;
            --success-text: #047857;
            --error-bg: #FEF2F2;
            --error-border: #EF4444;
            --error-text: #B91C1C;
        }

        * {
            box-sizing: border-box;
            touch-action: manipulation;
        }

        body {
            margin: 0;
            background-color: var(--bg-body);
            color: var(--text-main);
            font-family: 'M PLUS Rounded 1c', sans-serif;
            padding-bottom: 40px;
            line-height: 1.6;
        }

        /* --- Header --- */
        .app-header {
            background: var(--bg-surface);
            padding: 12px 16px;
            border-bottom: 1px solid var(--border);
            position: sticky;
            top: 0;
            z-index: 100;
            display: flex;
            align-items: center;
            justify-content: space-between;
        }

        .back-link {
            color: var(--text-sub);
            text-decoration: none;
            display: flex;
            align-items: center;
            font-weight: 700;
            font-size: 1.4rem;
        }

        /* --- Tab Navigation --- */
        .tab-nav {
            display: flex;
            background: var(--bg-surface);
            padding: 8px 16px 0;
            border-bottom: 1px solid var(--border);
            position: sticky;
            top: 50px;
            z-index: 90;
        }

        .tab-btn {
            font-size: 0.85rem;
            flex: 1;
            text-align: center;
            padding: 12px;
            font-weight: 700;
            color: var(--text-sub);
            border-bottom: 3px solid transparent;
            cursor: pointer;
            transition: all 0.2s;
            background: none;
            border-top: none;
            border-left: none;
            border-right: none;
        }

        .tab-btn.active {
            color: var(--theme-color);
            border-bottom-color: var(--theme-color);
        }

        /* --- Content Area --- */
        .content-area {
            display: none;
            max-width: 800px;
            margin: 0 auto;
            padding: 24px 16px;
            animation: fadeIn 0.3s ease;
        }

        .content-area.active {
            display: block;
        }

        @keyframes fadeIn {
            from {
                opacity: 0;
                transform: translateY(5px);
            }

            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        /* --- Typography --- */
        h1 {
            font-size: 1.4rem;
            margin: 0 0 16px;
            line-height: 1.4;
            color: var(--text-main);
        }

        h2 {
            font-size: 1.1rem;
            border-left: 6px solid var(--theme-color);
            padding-left: 12px;
            margin: 40px 0 20px;
            color: var(--text-main);
            display: flex;
            align-items: center;
        }

        h3 {
            font-size: 1.1rem;
            margin: 24px 0 12px;
            color: var(--text-main);
        }

        p {
            line-height: 1.8;
            color: #334155;
            margin-bottom: 16px;
            font-size: 1rem;
        }

        ul {
            margin-bottom: 16px;
            color: #334155;
        }

        li {
            margin-bottom: 8px;
        }

        /* --- Highlight Box --- */
        .highlight-box {
            background: var(--theme-light);
            border: 2px solid var(--theme-color);
            border-radius: 12px;
            padding: 20px;
            margin: 24px 0;
            position: relative;
        }

        .highlight-label {
            position: absolute;
            top: -12px;
            left: 16px;
            background: var(--theme-color);
            color: white;
            font-size: 0.75rem;
            font-weight: 700;
            padding: 2px 10px;
            border-radius: 20px;
        }

        /* --- Example Box --- */
        .example-box {
            background: #F1F5F9;
            border-left: 4px solid #94A3B8;
            border-radius: 8px;
            padding: 16px;
            margin: 16px 0;
        }

        .ex-text-en {
            font-family: 'Inter', sans-serif;
            font-weight: 600;
            font-size: 1rem;
            color: #1E293B;
            margin-bottom: 4px;
        }

        .ex-text-jp {
            font-size: 0.9rem;
            color: #64748B;
        }

        .note-text {
            font-size: 0.9rem;
            color: #64748B;
            margin-top: 4px;
        }

        /* --- Listening Section --- */
        .example-item {
            background: var(--bg-surface);
            border: 1px solid var(--border);
            border-radius: 12px;
            padding: 12px 16px;
            margin-bottom: 12px;
            display: flex;
            align-items: center;
            gap: 16px;
        }

        .play-btn-sm {
            background: var(--theme-light);
            color: var(--theme-color);
            border: none;
            width: 44px;
            height: 44px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 1.4rem;
            cursor: pointer;
            flex-shrink: 0;
            transition: transform 0.1s;
        }

        .play-btn-sm:active {
            transform: scale(0.95);
            background: #DBEAFE;
        }

        /* --- Practice Quiz Styles --- */
        .quiz-container {
            max-width: 800px;
            margin: 0 auto;
        }

        .quiz-header {
            padding: 0 0 8px 0;
            margin-bottom: 8px;
        }

        .progress-container {
            margin: 0;
        }

        .progress-label {
            display: flex;
            justify-content: space-between;
            font-size: 0.85rem;
            margin-bottom: 6px;
            color: var(--text-sub);
        }

        .progress-bar {
            height: 4px;
            background: var(--border);
            border-radius: 2px;
            overflow: hidden;
        }

        .progress-fill {
            height: 100%;
            background: var(--theme-color);
            width: 0%;
            transition: width 0.4s ease;
            border-radius: 2px;
        }

        /* --- Quiz Card --- */
        .quiz-card {
            background: var(--bg-surface);
            border-radius: 20px;
            box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
            padding: 8px 24px;
        }

        .question-jp {
            font-size: 1.1rem;
            font-weight: 700;
            margin-top: 12px;
            margin-bottom: 12px;
            padding-left: 16px;
            text-align: left;
            color: var(--text-main);
            min-height: 2em;
            display: flex;
            align-items: center;
            justify-content: flex-start;
        }

        .answer-display {
            margin-bottom: 24px;
        }

        .answer-box {
            background: #F8FAFC;
            border: 2px solid var(--border);
            border-radius: 12px;
            min-height: 70px;
            padding: 16px;
            display: flex;
            flex-wrap: wrap;
            gap: 8px;
            align-items: center;
            font-family: 'Inter', sans-serif;
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--text-main);
            transition: all 0.3s;
            position: relative;
        }

        .answer-box-feedback {
            position: absolute;
            top: 8px;
            right: 12px;
            display: flex;
            align-items: center;
            gap: 6px;
            font-size: 0.9rem;
            font-weight: 700;
            opacity: 0;
            transition: opacity 0.3s;
        }

        .answer-box-feedback.show {
            opacity: 1;
        }

        .answer-box-feedback i {
            font-size: 1.3rem;
        }

        .answer-box.correct {
            background: var(--success-bg);
            border-color: var(--success-border);
            color: var(--success-text);
        }

        .answer-box.incorrect {
            background: var(--error-bg);
            border-color: var(--error-border);
            color: var(--error-text);
        }

        .answer-box:empty::before {
            color: #94A3B8;
            font-size: 0.95rem;
            font-weight: 400;
        }

        /* --- Word Chips --- */
        .word-pool {
            display: flex;
            flex-wrap: wrap;
            gap: 10px;
            justify-content: center;
            margin-bottom: 24px;
        }

        .word-chip {
            background: white;
            border: 2px solid #CBD5E1;
            padding: 12px 20px;
            border-radius: 10px;
            font-family: 'Inter', sans-serif;
            font-weight: 600;
            font-size: 1rem;
            cursor: pointer;
            user-select: none;
            transition: all 0.15s;
            color: var(--text-main);
        }

        .word-chip:hover:not(:disabled) {
            box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
        }

        .word-chip:active:not(:disabled) {
            transform: translateY(1px);
            border-bottom-width: 2px;
        }

        .word-chip:disabled {
            color: #CBD5E1;
            cursor: not-allowed;
            opacity: 0.5;
        }

        /* --- Action Buttons --- */
        .action-buttons {
            display: flex;
            gap: 12px;
            margin-bottom: 24px;
        }

        .btn {
            flex: 1;
            padding: 14px 24px;
            border: none;
            border-radius: 10px;
            font-weight: 700;
            font-size: 1rem;
            cursor: pointer;
            transition: all 0.2s;
            font-family: 'M PLUS Rounded 1c', sans-serif;
        }

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

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

        .btn-secondary {
            background: #E5E7EB;
            color: #64748B;
        }

        .btn-secondary:hover {
            background: #D1D5DB;
        }

        .btn-warning {
            background: #E5E7EB;
            color: #64748B;
        }

        .btn-warning:hover {
            background: #D1D5DB;
        }

        .btn-danger {
            background: #EF4444;
            color: white;
        }

        .btn-danger:hover {
            background: #DC2626;
        }

        .check-btn {
            width: 200px;
            margin: 0 auto;
            font-size: 1.1rem;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: 8px;
        }

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

            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        .feedback-message.correct {
            background: var(--success-bg);
            color: var(--success-text);
            border: 2px solid var(--success-border);
        }

        .feedback-message.incorrect {
            background: var(--error-bg);
            color: var(--error-text);
            border: 2px solid var(--error-border);
        }

        /* --- Results Section --- */
        .results-container {
            background: var(--bg-surface);
            border-radius: 20px;
            padding: 32px 24px;
            box-shadow: 0 4px 20px rgba(0, 0, 0, 0.05);
            text-align: center;
        }

        .results-title {
            font-size: 1.5rem;
            font-weight: 700;
            margin-bottom: 24px;
            color: var(--text-main);
        }

        .results-score {
            font-size: 3rem;
            font-weight: 800;
            color: var(--theme-color);
            margin-bottom: 8px;
        }

        .results-label {
            font-size: 1rem;
            color: var(--text-sub);
            margin-bottom: 32px;
        }

        .missed-list {
            text-align: left;
            margin-top: 32px;
        }

        .missed-list-title {
            font-size: 1.1rem;
            font-weight: 700;
            margin-bottom: 16px;
            color: var(--text-main);
        }

        .missed-item {
            background: #F8FAFC;
            border: 1px solid var(--border);
            border-radius: 12px;
            padding: 16px;
            margin-bottom: 12px;
        }

        .missed-question {
            font-weight: 700;
            color: var(--text-main);
            margin-bottom: 8px;
        }

        .missed-answer {
            font-family: 'Inter', sans-serif;
            color: var(--success-text);
            margin-bottom: 4px;
        }

        .missed-your-answer {
            font-family: 'Inter', sans-serif;
            color: var(--error-text);
        }

        .answer-comparison {
            display: flex;
            flex-direction: column;
            gap: 8px;
            margin-top: 8px;
        }

        .answer-row {
            display: flex;
            align-items: center;
            gap: 8px;
            font-size: 0.9rem;
        }

        .answer-row i {
            font-size: 1.2rem;
        }

        /* --- Hidden State --- */
        .hidden {
            display: none !important;
        }