* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }
        body {
            background: #f0f5fa;
            font-family: system-ui, 'Segoe UI', 'Inter', sans-serif;
            font-size: 1.125rem;
            padding: 1.5rem;
        }
        .app {
            max-width: 1400px;
            margin: 0 auto;
            background: white;
            box-shadow: 0 20px 35px -12px rgba(0,0,0,0.1);
            overflow: hidden;
        }
        .tab-bar {
            display: flex;
            align-items: center;
            padding: 0.6rem 1.5rem;
            background: white;
            border-bottom: 1px solid #e2eaf1;
            position: relative;
        }
        .nav-logo {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            text-decoration: none;
            font-size: 1.1rem;
            font-weight: 700;
            color: #1e6f8c;
            white-space: nowrap;
            flex-shrink: 0;
        }
        .nav-logo img {
            width: 28px;
            height: 28px;
        }
        .nav-items {
            display: flex;
            align-items: center;
            gap: 0.3rem;
            margin-left: auto;
        }
        .hamburger-btn {
            display: none;
            background: none;
            border: none;
            cursor: pointer;
            padding: 0.5rem;
            margin-left: auto;
            flex-direction: column;
            gap: 4px;
        }
        .hamburger-btn span {
            display: block;
            width: 22px;
            height: 2px;
            background: #2c5a74;
            border-radius: 2px;
            transition: all 0.3s;
        }
        .hamburger-btn.active span:nth-child(1) {
            transform: translateY(6px) rotate(45deg);
        }
        .hamburger-btn.active span:nth-child(2) {
            opacity: 0;
        }
        .hamburger-btn.active span:nth-child(3) {
            transform: translateY(-6px) rotate(-45deg);
        }
        .tab {
            background: none;
            border: none;
            padding: 0.6rem 1.2rem;
            font-size: 0.95rem;
            font-weight: 600;
            border-radius: 1rem;
            cursor: pointer;
            color: #2c5a74;
            transition: all 0.2s;
            white-space: nowrap;
        }
        .tab.active {
            background: #1e6f8c;
            color: white;
        }
        
        
        .content {
            padding: 2rem;
        }
        /* 卡片样式 */
        .section {
            margin-bottom: 3.5rem;
        }
        .tense-heading {
            font-size: 2rem;
            font-weight: 800;
            color: #1a4f6a;
            display: flex;
            align-items: center;
            gap: 1rem;
            margin-bottom: 2rem;
            padding-bottom: 1rem;
            letter-spacing: 0.05em;
        }
        .tense-name-group {
            display: flex;
            align-items: baseline;
            flex-wrap: wrap;
            gap: 0.15em;
        }
        .tense-eng-name {
            font-size: 0.65em;
            font-weight: 500;
            color: #5a8a9f;
        }
        .heading-time-selector {
            display: flex;
            align-items: center;
            gap: 0.5rem;
            background: #f0f4f8;
            padding: 0.35rem 1rem;
            border-radius: 2rem;
            font-size: 0.9rem;
            font-weight: 600;
            color: #2c5a74;
            flex-shrink: 0;
            margin-left: auto;
        }
        .heading-time-selector select {
            padding: 0.3rem 0.8rem;
            border-radius: 1.5rem;
            border: 1px solid #cbdae4;
            background: white;
            font-weight: 500;
            font-size: 0.9rem;
            color: #2c5a74;
        }
        .section-title {
            font-size: 1.6rem;
            font-weight: 700;
            color: #1f5d7a;
            border-left: 5px solid #2c8dad;
            padding-left: 1rem;
            margin-bottom: 1rem;
        }
        .meaning-text {
            background: #f7fdfe;
            padding: 1.2rem 1.5rem;
            border-radius: 1rem;
            line-height: 2;
            border: 1px solid #ddecf2;
        }
        .case-list {
            background: #fef7e8;
            margin-top: 1rem;
            padding: 1.2rem 1.8rem;
            border-radius: 1rem;
            line-height: 1.8;
        }
        .case-list ul {
            margin-top: 0.5rem;
            margin-left: 20px;
        }
        .case-list li {
            margin: 0.5rem 0;
            line-height: 2;
        }
        .grammar-structure {
            background: #f6fafc;
            padding: 1.2rem 1.5rem;
            border-radius: 1rem;
        }
        .grammar-item {
            margin: 0.7rem 0;
            line-height: 1.8;
        }
        .grammar-item strong {
            background: #e2edf3;
            padding: 0.2rem 0.6rem;
            border-radius: 1rem;
            font-family: monospace;
        }
        .example-list {
            list-style: none;
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 1rem;
        }
        .example-item {
            background: #fafeff;
            margin: 0;
            padding: 1.2rem 1.4rem;
            border-radius: 1rem;
            border: 1px solid #deeaf1;
            line-height: 2.2;
        }
        .example-en {
            margin-bottom: 0.3rem;
        }
        .example-en strong {
            color: #1e6f8c;
            background: #e4f0f5;
            padding: 0 0.2rem;
        }
        .example-trans {
            margin-bottom: 0.2rem;
        }
        .quiz-item {
            background: #fafeff;
            margin: 1rem 0;
            padding: 1rem 1.2rem;
            border-radius: 1rem;
            border: 1px solid #deeaf1;
            display: flex;
            flex-wrap: wrap;
            align-items: flex-start;
            gap: 0.5rem;
            line-height: 2;
        }
        .quiz-item .quiz-text {
            flex: 1;
            min-width: 0;
        }
        .show-answer-btn {
            background: linear-gradient(135deg, #e8f4f8, #d5eaf2);
            border: 1px solid #b8d8e8;
            padding: 0.35rem 1.2rem;
            border-radius: 2rem;
            cursor: pointer;
            font-size: 0.85rem;
            font-weight: 600;
            color: #1e6f8c;
            transition: all 0.25s ease;
            white-space: nowrap;
            flex-shrink: 0;
            align-self: center;
        }
        .show-answer-btn:hover {
            background: linear-gradient(135deg, #d0ebf5, #b8ddef);
            box-shadow: 0 2px 8px rgba(30,111,140,0.15);
            transform: translateY(-1px);
        }
        .show-answer-btn:active {
            transform: translateY(0);
            box-shadow: none;
        }
        .answer-text {
            width: 100%;
            margin-top: 0.5rem;
            background: #e6f3ef;
            padding: 0.8rem 1rem;
            border-radius: 1rem;
            display: none;
            line-height: 1.9;
        }
        .answer-text.show {
            display: block;
        }
        /* 句型扩展卡片 */
        .expand-card {
            background: #f6fafc;
            padding: 1.2rem 1.5rem;
            border-radius: 1rem;
            margin-bottom: 1rem;
            border: 1px solid #e2ecf2;
        }
        .expand-card-title {
            font-size: 1.05rem;
            font-weight: 700;
            margin-bottom: 0.6rem;
        }
        .expand-card-body {
            line-height: 2.2;
        }
        /* 语法技巧 - 表格型条目 */
        .grammar-table-card {
            margin-left: 1rem;
            margin-bottom: 1rem;
            background: #fafefe;
            padding: 1rem 1.2rem;
            border-radius: 1rem;
            border: 1px solid #e2ecf2;
        }
        .grammar-table-card strong {
            font-size: 1rem;
        }
        .grammar-table-item {
            display: flex;
            gap: 1rem;
            padding: 0.5rem 0;
            border-bottom: 1px dashed #e0ecf0;
            line-height: 1.8;
        }
        .grammar-table-item:last-child {
            border-bottom: none;
        }
        .grammar-rule-title {
            font-weight: 700;
            font-size: 1.05rem;
            color: #1e6f8c;
            display: block;
            margin-bottom: 0.3rem;
        }
        .grammar-examples-label {
            font-weight: 700;
            color: inherit;
            margin-top: 0.4rem;
            margin-bottom: 0.2rem;
        }
        .grammar-example-list {
            list-style: disc;
            padding-left: 1.5rem;
            margin: 0.3rem 0 0 0;
        }
        .grammar-example-list li {
            font-size: 1rem;
            color: inherit;
            margin-bottom: 0.3rem;
            line-height: 1.8;
        }
        .grammar-example-list li:last-child {
            margin-bottom: 0;
        }
        .grammar-items-grid {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 1rem;
        }
        .grammar-items-grid .grammar-table-card {
            margin-left: 0;
            margin-bottom: 0;
        }
        .grammar-table-item .gt-tense {
            font-weight: 600;
            color: #1e6f8c;
            min-width: 6rem;
            flex-shrink: 0;
        }
        .grammar-table-item .gt-struct {
            color: #3a6b7f;
            min-width: 10rem;
            flex-shrink: 0;
        }
        .grammar-table-item .gt-example {
            color: #555;
            flex: 1;
        }
        /* 时态实战 */
        .practice-item {
            border: 1px solid #cde0ea;
            margin: 1.2rem 0;
            padding: 1.2rem 1.4rem;
            border-radius: 1rem;
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 0.8rem;
            background: #fcfefe;
        }
        .practice-item .prac-text {
            flex: 1;
            min-width: 0;
            font-size: 1rem;
            line-height: 1.8;
        }
        .prac-btn {
            background: linear-gradient(135deg, #e8f4f8, #d5eaf2);
            border: 1px solid #b8d8e8;
            padding: 0.4rem 1.4rem;
            border-radius: 2rem;
            cursor: pointer;
            font-size: 0.85rem;
            font-weight: 600;
            color: #1e6f8c;
            transition: all 0.25s ease;
            white-space: nowrap;
            flex-shrink: 0;
        }
        .prac-btn:hover {
            background: linear-gradient(135deg, #d0ebf5, #b8ddef);
            box-shadow: 0 2px 8px rgba(30,111,140,0.15);
            transform: translateY(-1px);
        }
        .prac-btn:active {
            transform: translateY(0);
            box-shadow: none;
        }
        .prac-answer {
            width: 100%;
            display: none;
            margin-top: 0.3rem;
            background: #e9f5f1;
            padding: 0.8rem 1rem;
            border-radius: 1rem;
            line-height: 1.9;
            border: 1px solid #d0e8e0;
        }
        .prac-answer.show {
            display: block;
        }
        /* 16时态概览 - 4×4 矩阵表格 */
        .matrix-card {
            border-radius: 0.5rem;
            box-shadow: 0 6px 24px rgba(0,0,0,0.06);
            border: 1px solid #d8e8f0;
        }
        .matrix-scroll-wrapper {
            overflow-x: auto;
            -webkit-overflow-scrolling: touch;
        }
        .matrix-table {
            width: 100%;
            border-collapse: separate;
            border-spacing: 0;
            border-radius: 0.5rem;
        }
        .matrix-table th,
        .matrix-table td {
            padding: 0;
            border: 1px solid #e2edf4;
        }
        /* 表格四角圆角 */
        .matrix-table thead th:first-child { border-radius: 0.5rem 0 0 0; }
        .matrix-table thead th:last-child  { border-radius: 0 0.5rem 0 0; }
        .matrix-table tbody tr:last-child th        { border-radius: 0 0 0 0.5rem; }
        .matrix-table tbody tr:last-child td:last-child { border-radius: 0 0 0.5rem 0; }
        /* 表头（列标题：一般/进行/完成/完成进行） */
        .matrix-table thead th {
            background: linear-gradient(135deg, #8a9daa, #a0b3bd);
            color: white;
            padding: 1rem 0.8rem;
            font-size: 1.05rem;
            font-weight: 700;
            text-align: center;
            letter-spacing: 0.05em;
            border: none;
        }
        .matrix-table thead th.corner-cell {
            background: linear-gradient(135deg, #748a97, #8a9daa);
            font-size: 0.92rem;
            font-weight: 600;
            color: #e8f0f4;
            text-align: center;
            white-space: nowrap;
        }
        /* 行标题（时间维度：现在/过去/将来/过去将来） */
        .matrix-table tbody th {
            background: #edf4f9;
            padding: 1rem 1.2rem;
            font-size: 1.05rem;
            font-weight: 700;
            color: #1e6f8c;
            text-align: center;
            vertical-align: middle;
            white-space: nowrap;
            border-right: 2px solid #d0e2ec;
        }
        /* 单元格 */
        .matrix-table tbody td {
            background: #fafdfe;
            padding: 1.1rem 1rem;
            text-align: center;
            vertical-align: middle;
            cursor: default;
            transition: all 0.2s ease;
            position: relative;
        }
        .matrix-table tbody td:hover {
            background: #e4f2f8;
            box-shadow: inset 0 0 0 2px #2c8dad;
            z-index: 2;
        }
        /* 行高亮 */
        .matrix-table tbody tr:hover th {
            background: #dceaf2;
        }
        .matrix-table tbody tr:hover td {
            background: #eef7fb;
        }
        .matrix-table tbody tr:hover td:hover {
            background: #d8eef6;
        }
        .matrix-cell-name {
            display: block;
            font-size: 1.1rem;
            font-weight: 700;
            color: #1e6f8c;
            margin-bottom: 0.4rem;
        }
        .matrix-cell-struct {
            display: block;
            margin-bottom: 0.5rem;
        }
        .matrix-cell-struct .struct-pill {
            display: inline-block;
            background: #e4f0f5;
            color: #1e6f8c;
            font-family: 'Consolas', 'Menlo', monospace;
            font-size: 0.88rem;
            padding: 0.2rem 0.6rem;
            border-radius: 1rem;
            margin: 0.12rem 0.1rem;
            white-space: nowrap;
        }
        .matrix-cell-desc {
            display: block;
            font-size: 0.92rem;
            color: #4a6a7a;
            line-height: 1.6;
            margin-top: 0.3rem;
        }
        /* 通用表格回退（其他页面） */
        table {
            width: 100%;
            border-collapse: collapse;
        }
        th, td {
            border: 1px solid #cde0ea;
            padding: 10px;
            text-align: left;
            vertical-align: top;
        }
        th {
            background: #eaf3f9;
        }
        /* 首页欢迎引导区 */
        .welcome-section {
            margin-bottom: 2.5rem;
        }
        .welcome-hero {
            background: linear-gradient(135deg, #f0f8fc 0%, #e8f4f0 100%);
            border-radius: 1.2rem;
            padding: 2rem 2.5rem;
            margin-bottom: 1.8rem;
            border: 1px solid #d8eaf0;
        }
        .welcome-title {
            font-size: 1.6rem;
            font-weight: 800;
            color: #1a4f6a;
            margin-bottom: 0.6rem;
        }
        .welcome-desc {
            font-size: 1rem;
            color: #4a6a7a;
            line-height: 1.9;
        }
        .guide-grid {
            display: grid;
            grid-template-columns: repeat(3, 1fr);
            gap: 1rem;
        }
        .guide-card {
            background: #fafdfe;
            border-radius: 1rem;
            padding: 1.4rem 1.5rem;
            border: 1px solid #e2edf4;
            transition: transform 0.2s ease, box-shadow 0.2s ease;
        }
        .guide-card:hover {
            transform: translateY(-3px);
            box-shadow: 0 8px 20px rgba(0,0,0,0.08);
        }
        .guide-card-icon {
            font-size: 1.6rem;
            margin-bottom: 0.5rem;
        }
        .guide-card-title {
            font-size: 1.05rem;
            font-weight: 700;
            color: #1a5a74;
            margin-bottom: 0.4rem;
        }
        .guide-card-text {
            font-size: 0.9rem;
            color: #5a7a8a;
            line-height: 1.7;
        }
        /* 首页学习数据概览 */
        .stats-section {
            margin-top: 2.5rem;
        }
        .stats-title {
            font-size: 1.3rem;
            font-weight: 700;
            color: #1a5a74;
            margin-bottom: 1.2rem;
            display: flex;
            align-items: center;
            gap: 0.5rem;
        }
        .stats-grid {
            display: grid;
            grid-template-columns: repeat(4, 1fr);
            gap: 1rem;
        }
        .stat-card {
            background: #fafdfe;
            border-radius: 1rem;
            padding: 1.5rem 1.2rem;
            border: 1px solid #e2edf4;
            text-align: center;
            transition: transform 0.2s ease, box-shadow 0.2s ease;
        }
        .stat-card:hover {
            transform: translateY(-3px);
            box-shadow: 0 8px 20px rgba(0,0,0,0.08);
        }
        .stat-number {
            font-size: 2.4rem;
            font-weight: 800;
            background: linear-gradient(135deg, #1e6f8c, #2a8aaa);
            background-clip: text;
            -webkit-background-clip: text;
            color: transparent;
            line-height: 1.2;
        }
        .stat-label {
            font-size: 0.9rem;
            color: #5a7a8a;
            margin-top: 0.4rem;
            font-weight: 500;
        }
        .hidden {
            display: none;
        }
        /* 卡片悬停效果 - 统一抬起 + 阴影 */
        .meaning-text,
        .case-list,
        .grammar-structure,
        .expand-card,
        .grammar-table-card,
        .example-item,
        .quiz-item,
        .practice-item {
            transition: transform 0.2s ease, box-shadow 0.2s ease;
        }
        .meaning-text:hover,
        .case-list:hover,
        .grammar-structure:hover,
        .expand-card:hover,
        .grammar-table-card:hover,
        .example-item:hover,
        .quiz-item:hover,
        .practice-item:hover {
            transform: translateY(-3px);
            box-shadow: 0 8px 20px rgba(0,0,0,0.08);
        }
        @media (max-width: 700px) {
            body { padding: 0; font-size: 0.95rem; }
            .app { box-shadow: none; }
            .tab-bar {
                padding: 0.5rem 0.8rem;
                flex-wrap: wrap;
            }
            .nav-logo { font-size: 1rem; }
            .nav-logo img { width: 24px; height: 24px; }
            .hamburger-btn {
                display: flex;
            }
            .nav-items {
                display: none;
                flex-direction: column;
                width: 100%;
                gap: 0.2rem;
                padding-top: 0.5rem;
                border-top: 1px solid #e2eaf1;
                margin-top: 0.5rem;
                margin-left: 0;
            }
            .nav-items.open {
                display: flex;
            }
            .nav-items .tab {
                padding: 0.55rem 0.8rem;
                font-size: 0.9rem;
                text-align: left;
                width: 100%;
                border-radius: 0.5rem;
            }
            .content { padding: 0.8rem; }
            .section { margin-bottom: 2.5rem; }
            .section-title { font-size: 1.2rem; }
            .tense-heading {
                font-size: 1.5rem;
                flex-direction: row;
                flex-wrap: wrap;
                align-items: center;
                gap: 0.5rem;
            }
            .tense-name-group {
                flex-direction: column;
                gap: 0.2rem;
                flex: 1;
                min-width: 0;
            }
            .tense-eng-name {
                font-size: 0.85rem;
            }
            .heading-time-selector {
                margin-left: auto;
                margin-top: 0;
                padding: 0;
                background: none;
            }
            .heading-time-selector .time-label {
                display: none;
            }
            .matrix-table { min-width: 600px; }
            .matrix-table th,
            .matrix-table td { padding: 0.7rem 0.6rem; }
            .matrix-cell-name { font-size: 0.95rem; }
            .matrix-cell-struct .struct-pill { font-size: 0.78rem; padding: 0.15rem 0.45rem; }
            .matrix-cell-desc { font-size: 0.82rem; }
            .example-list { grid-template-columns: 1fr; }
            .guide-grid { grid-template-columns: 1fr; }
            .grammar-items-grid { grid-template-columns: 1fr; }
            .welcome-hero { padding: 1.2rem; }
            .welcome-title { font-size: 1.3rem; }
            .stats-grid { grid-template-columns: repeat(2, 1fr); }
            .meaning-text, .case-list, .grammar-structure,
            .expand-card, .grammar-table-card, .example-item,
            .quiz-item, .practice-item { padding: 1rem; }
            .grammar-table-card { margin-left: 0; }
            .grammar-example-list li { font-size: 0.9rem; }
            .grammar-rule-title { font-size: 0.95rem; }
        }
        .tab { text-decoration: none; }