:root {
            --primary-color: #1e40af;
            --primary-hover: #1e3a8a;
            --bg-color: #f0f0f0;
            --sidebar-bg: #f9f9f9;
            --card-bg: #ffffff;
            --border-color: #ccc;
            --text-main: #333;
            --text-muted: #666;
        }

        body {
            font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
            margin: 0;
            padding: 0;
            background-color: var(--bg-color);
            color: var(--text-main);
            display: flex;
        }

        h1,
        h2,
        h3 {
            color: var(--primary-color);
        }

        h1 {
            text-align: center;
        }

        .sidebar {
            width: 240px;
            height: 100vh;
            background-color: var(--sidebar-bg);
            position: fixed;
            padding: 20px 0;
            box-shadow: 2px 0 5px rgba(0, 0, 0, 0.1);
            overflow-y: auto;
            z-index: 100;
        }

        .sidebar h2 {
            padding: 0 20px;
            font-size: 20px;
        }

        .nav-menu {
            display: flex;
            flex-direction: column;
            gap: 5px;
            padding: 0 10px;
        }

        .nav-btn {
            background: none;
            border: none;
            text-align: left;
            padding: 12px 15px;
            cursor: pointer;
            font-size: 15px;
            color: var(--primary-color);
            border-radius: 6px;
            transition: background 0.2s;
        }

        .nav-btn:hover,
        .nav-btn.active {
            background-color: rgba(30, 64, 175, 0.1);
        }

        .content {
            margin-left: 240px;
            padding: 30px;
            width: 100%;
            min-height: 100vh;
            box-sizing: border-box;
            background-color: rgba(255, 255, 255, 0.6);
        }

        @media (max-width: 768px) {
            body {
                flex-direction: column;
            }

            .sidebar {
                width: 100%;
                height: auto;
                position: relative;
            }

            .content {
                margin-left: 0;
                padding: 15px;
            }
        }

        .info-box {
            background: var(--card-bg);
            border-radius: 8px;
            padding: 16px 20px;
            margin-bottom: 16px;
            box-shadow: 0 2px 5px rgba(0, 0, 0, 0.04);
            border: 1px solid var(--border-color);
        }

        .status-text {
            font-size: 14px;
            color: var(--text-muted);
        }

        .status-text strong {
            color: var(--primary-color);
        }

        .list-container {
            margin-top: 10px;
            background: var(--card-bg);
            border-radius: 8px;
            border: 1px solid var(--border-color);
            max-height: 70vh;
            overflow-y: auto;
        }

        .item-card {
            padding: 12px 16px;
            border-bottom: 1px solid #eee;
        }

        .item-card:last-child {
            border-bottom: none;
        }

        .item-header {
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            align-items: baseline;
            gap: 4px 10px;
            margin-bottom: 4px;
        }

        .item-title {
            font-weight: 600;
            font-size: 17px;
        }

        .item-meta {
            font-size: 12px;
            color: var(--text-muted);
        }

        .item-body {
            font-size: 14px;
            color: var(--text-main);
            line-height: 1.6;
            white-space: pre-wrap;
        }

        .item-sub {
            font-size: 13px;
            color: var(--text-muted);
            margin-top: 4px;
            white-space: pre-wrap;
        }

        .badge {
            display: inline-block;
            padding: 2px 8px;
            font-size: 11px;
            border-radius: 999px;
            background: rgba(30, 64, 175, 0.08);
            color: var(--primary-color);
        }

        .loading {
            text-align: center;
            padding: 40px 10px;
            color: var(--text-muted);
        }

        .error {
            text-align: center;
            padding: 40px 10px;
            color: #b91c1c;
        }

        .json-raw {
            margin-top: 6px;
            font-size: 12px;
            background: #f3f4f6;
            border-radius: 4px;
            padding: 6px 8px;
            white-space: pre-wrap;
            word-break: break-all;
        }

        /* 文法用：単元ごとの折りたたみ表示 */
        .unit-toolbar {
            display: flex;
            justify-content: flex-end;
            gap: 8px;
            margin-bottom: 8px;
        }

        .unit-toolbar button {
            padding: 4px 10px;
            font-size: 12px;
            border-radius: 999px;
            border: 1px solid var(--border-color);
            background: #f9fafb;
            cursor: pointer;
        }

        .grammar-unit {
            border-bottom: 1px solid #e5e7eb;
        }

        .unit-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 10px 14px;
            cursor: pointer;
            background: #f9fafb;
        }

        .unit-header:hover {
            background: #eff6ff;
        }

        .unit-title {
            font-weight: 600;
            color: var(--primary-color);
        }

        .unit-count {
            font-size: 12px;
            color: var(--text-muted);
        }

        .unit-toggle {
            margin-left: 12px;
            font-size: 14px;
            color: var(--primary-color);
        }

        .unit-body {
            padding: 4px 10px 10px;
        }

        /* クイズ用CSS */
        .quiz-setup {
            padding: 20px;
            background: var(--card-bg);
            border-radius: 8px;
            border: 1px solid var(--border-color);
            margin-top: 10px;
        }

        .quiz-setup h3 {
            margin-top: 0;
            color: var(--primary-color);
        }

        .form-group {
            margin-bottom: 15px;
        }

        .form-group label {
            display: block;
            margin-bottom: 5px;
            font-weight: 500;
        }

        .form-group select {
            width: 100%;
            padding: 8px;
            border: 1px solid var(--border-color);
            border-radius: 4px;
            font-size: 15px;
            background: white;
        }

        .btn-start {
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 10px 20px;
            font-size: 16px;
            border-radius: 6px;
            cursor: pointer;
            width: 100%;
            transition: background 0.2s;
        }

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

        .quiz-container {
            background: var(--card-bg);
            border-radius: 8px;
            border: 1px solid var(--border-color);
            padding: 24px;
            margin-top: 10px;
            min-height: 300px;
        }

        .quiz-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 20px;
            border-bottom: 2px solid #eee;
            padding-bottom: 10px;
        }

        .quiz-progress {
            font-size: 14px;
            color: var(--text-muted);
            font-weight: 600;
        }

        .quiz-question {
            font-size: 28px;
            text-align: center;
            margin: 30px 0;
            font-weight: bold;
            color: var(--text-main);
            min-height: 80px;
            display: flex;
            align-items: center;
            justify-content: center;
        }

        .quiz-options {
            display: flex;
            flex-direction: column;
            gap: 12px;
        }

        .quiz-option {
            background: #f8fafc;
            border: 2px solid #e2e8f0;
            border-radius: 8px;
            padding: 16px;
            font-size: 18px;
            text-align: center;
            cursor: pointer;
            transition: all 0.2s;
        }

        .quiz-option:hover:not(:disabled) {
            background: #edf2f7;
            border-color: #cbd5e0;
        }

        .quiz-option.correct {
            background: #c6f6d5;
            border-color: #48bb78;
            color: #22543d;
        }

        .quiz-option.wrong {
            background: #fed7d7;
            border-color: #f56565;
            color: #742a2a;
        }

        .quiz-option:disabled {
            cursor: not-allowed;
            opacity: 0.7;
        }

        .quiz-input-container {
            display: flex;
            flex-direction: column;
            gap: 15px;
            align-items: center;
        }

        .quiz-input {
            width: 100%;
            max-width: 400px;
            padding: 12px 15px;
            font-size: 20px;
            border: 2px solid var(--border-color);
            border-radius: 8px;
            text-align: center;
        }

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

        .quiz-submit-btn {
            background-color: var(--primary-color);
            color: white;
            border: none;
            padding: 12px 30px;
            font-size: 16px;
            border-radius: 6px;
            cursor: pointer;
            transition: background 0.2s;
            flex: 1;
        }

        .quiz-submit-btn:hover {
            background-color: var(--primary-hover);
        }

        .quiz-skip-btn {
            background-color: white;
            color: var(--text-muted);
            border: 2px solid var(--border-color);
            padding: 12px 30px;
            font-size: 16px;
            border-radius: 6px;
            cursor: pointer;
            transition: background 0.2s;
            flex: 1;
        }

        .quiz-skip-btn:hover {
            background-color: #f1f5f9;
        }

        .quiz-input-actions {
            display: flex;
            gap: 10px;
            width: 100%;
            max-width: 400px;
        }

        .quiz-feedback {
            margin-top: 20px;
            padding: 15px;
            border-radius: 8px;
            display: none;
            background: #f1f5f9;
            border-left: 4px solid var(--primary-color);
        }

        .quiz-next-btn {
            background-color: var(--text-main);
            color: white;
            border: none;
            padding: 12px 24px;
            font-size: 16px;
            border-radius: 6px;
            cursor: pointer;
            margin-top: 20px;
            display: none;
            float: right;
        }

        .quiz-next-btn:hover {
            background-color: #555;
        }

        .quiz-end-btn {
            background-color: white;
            color: #e53e3e;
            border: 1px solid #fc8181;
            padding: 6px 14px;
            font-size: 13px;
            border-radius: 4px;
            cursor: pointer;
            transition: background 0.2s;
        }

        .quiz-end-btn:hover {
            background-color: #fff5f5;
        }

        .clearfix::after {
            content: "";
            clear: both;
            display: table;
        }

        .quiz-result {
            text-align: center;
            padding: 40px 20px;
        }

        .quiz-result h2 {
            font-size: 32px;
            margin-bottom: 10px;
        }

        .quiz-result .score {
            font-size: 48px;
            font-weight: bold;
            color: var(--primary-color);
            margin: 20px 0;
        }

        .btn-restart {
            background: white;
            border: 2px solid var(--primary-color);
            color: var(--primary-color);
            padding: 10px 20px;
            font-size: 16px;
            border-radius: 6px;
            cursor: pointer;
            transition: all 0.2s;
        }

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

        /* 既習語彙リスト用 */
        .learned-vocab-container {
            margin-top: 20px;
            background: var(--card-bg);
            border-radius: 8px;
            border: 1px solid var(--border-color);
            padding: 20px;
        }

        .learned-vocab-title {
            font-size: 18px;
            font-weight: 600;
            margin-bottom: 12px;
            color: var(--text-main);
            border-bottom: 1px solid #eee;
            padding-bottom: 8px;
        }

        .learned-vocab-list {
            display: flex;
            flex-direction: column;
            gap: 8px;
        }

        .learned-vocab-item {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 8px 12px;
            border-radius: 6px;
            background: #f8fafc;
            border: 1px solid #e2e8f0;
            font-size: 15px;
        }

        .learned-vocab-item.correct {
            border-left: 4px solid #48bb78;
        }

        .learned-vocab-item.wrong {
            border-left: 4px solid #f56565;
        }

        .learned-vocab-word {
            font-weight: 600;
        }

        .learned-vocab-meaning {
            font-size: 13px;
            color: var(--text-muted);
            text-align: right;
        }