/* ============================================================
           设计系统：教育工具 · 克制 · 专业 · 支持暗色
           ============================================================ */
        :root {
            /* 主色 —— 沉稳藏青 */
            --primary: #1e3a8a;
            --primary-hover: #1d4ed8;
            --primary-light: #eff6ff;
            --primary-border: #bfdbfe;

            /* 六分类指示色（淡雅低饱和 · 互不重复） */
            --color-physics: #c08a5e;
            --color-others: #9b8cc0;
            --color-public: #7fb3ac;
            --color-class: #7fa8c4;
            --color-analysis: #86b598;
            --color-message: #b57b94;

            /* 中性色 */
            --bg: #f8fafc;
            --card-bg: #ffffff;
            --border: #e2e8f0;
            --border-light: #f1f5f9;
            --text-main: #111827;
            --text-secondary: #4b5563;
            --text-muted: #9ca3af;

            /* 表单/留言板 */
            --form-bg: #fefcf5;
            --form-border: #f0e6d3;
            --input-bg: #ffffff;

            /* 阴影 (仅hover使用) */
            --shadow-hover: 0 4px 12px rgba(0, 0, 0, 0.05);

            /* 圆角 */
            --radius-sm: 6px;
            --radius-md: 8px;
            --radius-lg: 10px;

            /* 过渡 */
            --ease: 0.15s ease;

            /* 侧边栏宽度 */
            --sidebar-width: 224px;

            /* Hero背景 */
            --hero-bg: #f0f5ff;
        }

        /* ===== 暗色主题变量 ===== */
        [data-theme="dark"] {
            --bg: #0f172a;
            --card-bg: #1e293b;
            --border: rgba(255, 255, 255, 0.08);
            --border-light: rgba(255, 255, 255, 0.06);

            --text-main: #e2e8f0;
            --text-secondary: #94a3b8;
            --text-muted: #64748b;

            --primary: #3b82f6;
            --primary-hover: #2563eb;
            --primary-light: rgba(59, 130, 246, 0.15);
            --primary-border: rgba(59, 130, 246, 0.3);

            --color-physics: #d9b38c;
            --color-others: #b9a9dd;
            --color-public: #98d0c9;
            --color-class: #9cc3df;
            --color-analysis: #a3d4b7;
            --color-message: #d9a8bd;

            --shadow-hover: 0 4px 12px rgba(0, 0, 0, 0.3);

            --form-bg: #271c19;
            --form-border: #7c2d12;
            --input-bg: #0f172a;

            --hero-bg: #0f172a;
        }

        /* ============================================================
           重置 & 全局
           ============================================================ */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
            background-color: var(--bg);
            color: var(--text-main);
            line-height: 1.6;
            -webkit-font-smoothing: antialiased;
            min-height: 100vh;
            transition: background-color 0.2s ease, color 0.2s ease;
        }

        a {
            text-decoration: none;
            color: inherit;
        }

        /* ============================================================
           关键帧 —— 仅保留必要淡入
           ============================================================ */
        @keyframes fadeIn {
            from {
                opacity: 0;
            }
            to {
                opacity: 1;
            }
        }

        @keyframes modalIn {
            from {
                opacity: 0;
                transform: scale(0.98);
            }
            to {
                opacity: 1;
                transform: scale(1);
            }
        }

        /* ============================================================
           顶部导航栏
           ============================================================ */
        .navbar {
            background: var(--card-bg);
            border-bottom: 1px solid var(--border);
            padding: 0.7rem 2rem;
            display: flex;
            align-items: center;
            justify-content: space-between;
            flex-wrap: nowrap;
            gap: 0.3rem 0.8rem;
            position: sticky;
            top: 0;
            z-index: 900;
            transition: background-color 0.2s ease, border-color 0.2s ease;
        }

        .navbar-logo {
            font-size: 2rem;
            font-weight: 700;
            color: #1A3C8C;
            /* 暗色下自动继承 text-main 或单独定义，但此处保留原色，可通过变量覆盖 */
            transition: color 0.2s ease;
        }
        [data-theme="dark"] .navbar-logo {
            color: var(--text-main);
        }

        .navbar-meta {
            display: flex;
            flex-wrap: nowrap;
            align-items: center;
            gap: 0.3rem 1.5rem;
            font-size: 0.85rem;
            color: var(--text-secondary);
            transition: color 0.2s ease;
        }

        .navbar-meta .update-badge,
        .navbar-meta .contact-badge {
            background: var(--border-light);
            padding: 0.2rem 0.9rem;
            border-radius: 20px;
            font-size: 0.78rem;
            color: var(--text-secondary);
            white-space: nowrap;
            transition: background-color 0.2s ease, color 0.2s ease;
        }

        .visit-count-badge {
            display: inline-flex;
            align-items: center;
            gap: 0.2rem;
            font-size: 0.78rem;
            color: var(--text-secondary);
            white-space: nowrap;
            margin-left: auto;
            transition: color 0.2s ease;
        }

        .visit-number {
            font-size: 2rem;
            font-weight: 700;
            color: var(--primary);
            line-height: 1.2;
            display: inline-block;
            vertical-align: middle;
            margin-top: -4px;
            transition: color 0.2s ease;
        }

        /* 主题切换按钮 */
        .theme-toggle {
            background: none;
            border: 1px solid var(--border);
            border-radius: var(--radius-sm);
            padding: 0.2rem 0.4rem;
            cursor: pointer;
            color: var(--text-secondary);
            display: inline-flex;
            align-items: center;
            transition: color 0.2s ease, border-color 0.2s ease;
            line-height: 1;
        }
        .theme-toggle:hover {
            color: var(--text-main);
            border-color: var(--text-muted);
        }
        .theme-toggle .sun-icon,
        .theme-toggle .moon-icon {
            display: block;
            width: 18px;
            height: 18px;
            stroke: currentColor;
            fill: none;
            stroke-width: 2;
        }
        [data-theme="dark"] .theme-toggle .sun-icon {
            display: none;
        }
        [data-theme="dark"] .theme-toggle .moon-icon {
            display: block;
        }
        [data-theme="light"] .theme-toggle .sun-icon {
            display: block;
        }
        [data-theme="light"] .theme-toggle .moon-icon {
            display: none;
        }

        /* ============================================================
           Hero 引导区
           ============================================================ */
        .hero {
            background: var(--hero-bg);
            text-align: center;
            padding: 2rem 1.5rem 1.8rem;
            border-bottom: 1px solid var(--border);
            animation: fadeIn 0.25s ease;
            transition: background-color 0.2s ease, border-color 0.2s ease;
        }

        .hero h1 {
            font-size: 1.5rem;
            font-weight: 600;
            color: var(--text-main);
            letter-spacing: 0.01em;
            margin-bottom: 0.2rem;
            transition: color 0.2s ease;
        }

        .hero p {
            font-size: 0.9rem;
            color: var(--text-secondary);
            max-width: 620px;
            margin: 0 auto;
            line-height: 1.5;
            transition: color 0.2s ease;
        }

        /* ============================================================
           主容器
           ============================================================ */
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 1.6rem 1.6rem 1rem 1.2rem;
            display: flex;
            gap: 1.8rem;
            align-items: flex-start;
            animation: fadeIn 0.25s ease;
        }

        /* ============================================================
           侧边栏
           ============================================================ */
        .sidebar {
            width: var(--sidebar-width);
            flex-shrink: 0;
            background: var(--card-bg);
            border: 1px solid var(--border);
            border-radius: var(--radius-lg);
            padding: 1.2rem 0.6rem;
            position: sticky;
            top: 84px;
            transition: background-color 0.2s ease, border-color 0.2s ease;
        }

        .sidebar-nav {
            list-style: none;
            display: flex;
            flex-direction: column;
            gap: 0.2rem;
        }

        .sidebar-nav li {
            position: relative;
        }

        .sidebar-nav .nav-item {
            display: flex;
            align-items: center;
            gap: 0.7rem;
            padding: 0.7rem 1rem 0.7rem 0.9rem;
            border-radius: var(--radius-md);
            cursor: pointer;
            font-weight: 500;
            font-size: 0.88rem;
            color: var(--text-secondary);
            transition: color 0.2s ease, background 0.2s ease;
            border: 1px solid transparent;
            user-select: none;
            position: relative;
        }

        .sidebar-nav .nav-item:hover {
            color: var(--primary);
            background: rgba(0, 0, 0, 0.02);
        }
        [data-theme="dark"] .sidebar-nav .nav-item:hover {
            background: rgba(255, 255, 255, 0.03);
            color: var(--primary);
        }

        .sidebar-nav .nav-item.active {
            color: var(--text-main);
            font-weight: 600;
            background: rgba(0, 0, 0, 0.02);
        }
        [data-theme="dark"] .sidebar-nav .nav-item.active {
            background: rgba(255, 255, 255, 0.03);
        }

        /* 左侧指示条 */
        .sidebar-nav .nav-item.active::before {
            content: "";
            position: absolute;
            left: -0.6rem;
            top: 50%;
            transform: translateY(-50%);
            width: 3px;
            height: 22px;
            border-radius: 0 2px 2px 0;
            transition: background 0.1s ease;
        }

        /* 分类指示色（变量已在暗色中提亮） */
        .nav-item.category-physics.active::before {
            background: var(--color-physics);
        }
        .nav-item.category-others.active::before {
            background: var(--color-others);
        }
        .nav-item.category-public.active::before {
            background: var(--color-public);
        }
        .nav-item.category-class.active::before {
            background: var(--color-class);
        }
        .nav-item.category-analysis.active::before {
            background: var(--color-analysis);
        }
        .nav-item.category-message.active::before {
            background: var(--color-message);
        }

        .nav-item.category-physics.active {
            color: var(--color-physics);
        }
        .nav-item.category-others.active {
            color: var(--color-others);
        }
        .nav-item.category-public.active {
            color: var(--color-public);
        }
        .nav-item.category-class.active {
            color: var(--color-class);
        }
        .nav-item.category-analysis.active {
            color: var(--color-analysis);
        }
        .nav-item.category-message.active {
            color: var(--color-message);
        }

        .nav-icon {
            font-size: 1.25rem;
            width: 1.5rem;
            flex-shrink: 0;
            display: inline-flex;
            align-items: center;
            justify-content: center;
            line-height: 1;
        }

        .nav-icon svg {
            display: block;
            width: 1.5rem;
            height: 1.5rem;
        }

        /* 其他学科教学书本图标视觉偏大，单独缩小 */
        .nav-item.category-others .nav-icon svg {
            width: 1.3rem;
            height: 1.3rem;
        }

        .nav-label {
            white-space: nowrap;
        }

        /* ============================================================
           内容面板
           ============================================================ */
        .content-area {
            flex: 1;
            min-width: 0;
        }

        .content-panel {
            display: none;
            animation: fadeIn 0.2s ease;
        }

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

        /* 面板标题 */
        .panel-header {
            display: flex;
            align-items: center;
            gap: 0.6rem;
            margin-bottom: 1.2rem;
            padding-bottom: 0.6rem;
            border-bottom: 1px solid var(--border);
            transition: border-color 0.2s ease;
        }

        .panel-header .panel-icon {
            font-size: 1.5rem;
            flex-shrink: 0;
            line-height: 1;
            display: flex;
            align-items: center;
        }

        .panel-header .panel-icon svg {
            display: block;
            width: 2rem;
            height: 2rem;
        }

        .panel-header h2 {
            font-size: 1.125rem;
            font-weight: 600;
            color: var(--text-main);
            letter-spacing: 0.01em;
            position: relative;
            margin-bottom: 0;
            transition: color 0.2s ease;
        }

        /* 标题下划线已注释掉，但变量已包含，如需启用可取消注释并调整颜色 */

        /* ============================================================
           学科标签页 (Segmented Control)
           ============================================================ */
        .subject-tabs {
            display: inline-flex;
            flex-wrap: wrap;
            gap: 0.25rem;
            margin-bottom: 1.2rem;
            border: 1px solid var(--border);
            border-radius: var(--radius-md);
            overflow: hidden;
            background: var(--card-bg);
            transition: border-color 0.2s ease, background 0.2s ease;
        }

        .subject-tab {
            padding: 0.3rem 0.9rem;
            font-size: 0.82rem;
            font-weight: 500;
            border: none;
            background: var(--card-bg);
            color: var(--text-secondary);
            cursor: pointer;
            transition: all 0.2s ease;
            font-family: inherit;
            border-right: 1px solid var(--border);
            flex: 0 0 auto;
        }

        .subject-tab:last-child {
            border-right: none;
        }

        .subject-tab:hover {
            background: var(--primary-light);
            color: var(--primary);
        }

        .subject-tab.active {
            background: var(--primary);
            color: #ffffff;
            font-weight: 500;
        }

        .subject-panel {
            display: none;
            animation: fadeIn 0.2s ease;
        }

        .subject-panel.active {
            display: block;
        }

        /* ============================================================
           工具卡片网格
           ============================================================ */
        .tool-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
            gap: 1rem;
        }

        /* ============================================================
           工具卡片
           ============================================================ */
        .tool-card {
            background: var(--card-bg);
            border: 1px solid var(--border);
            border-radius: var(--radius-lg);
            padding: 1rem 1.2rem 1.1rem;
            transition: transform 0.15s ease, box-shadow 0.15s ease, background 0.2s ease, border-color 0.2s ease;
            display: flex;
            flex-direction: column;
            position: relative;
            animation: fadeIn 0.2s ease;
        }

        .tool-card:hover {
            transform: translateY(-2px);
            box-shadow: var(--shadow-hover);
            border-color: var(--border);
        }

        .tool-card h3 {
            font-size: 1rem;
            font-weight: 600;
            margin-bottom: 0.3rem;
            color: var(--text-main);
            transition: color 0.2s ease;
        }

        .tool-card p {
            font-size: 0.875rem;
            color: var(--text-secondary);
            margin-bottom: 0.7rem;
            flex-grow: 1;
            line-height: 1.5;
            transition: color 0.2s ease;
        }

        .tool-meta {
            display: flex;
            flex-wrap: wrap;
            gap: 0.3rem 0.6rem;
            font-size: 0.75rem;
            color: var(--text-muted);
            margin-bottom: 0.7rem;
            transition: color 0.2s ease;
        }

        .tool-meta span {
            background: var(--border-light);
            padding: 0.1rem 0.6rem;
            border-radius: 12px;
            color: var(--text-secondary);
            border: 1px solid var(--border);
            transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
        }

        .tool-actions {
            display: flex;
            flex-wrap: wrap;
            gap: 0.4rem;
            align-items: center;
            margin-top: 0.2rem;
        }

        .tool-templates,
        .tool-guide {
            margin-top: 0.5rem;
            font-size: 0.78rem;
            display: flex;
            align-items: center;
            gap: 0.3rem;
            flex-wrap: wrap;
        }

        .tool-templates span,
        .tool-guide span {
            color: var(--text-muted);
            font-weight: 500;
            white-space: nowrap;
            transition: color 0.2s ease;
        }

        /* ============================================================
           按钮系统
           ============================================================ */
        .btn {
            display: inline-flex;
            align-items: center;
            gap: 0.3rem;
            padding: 0.35rem 1rem;
            border-radius: var(--radius-sm);
            font-size: 0.82rem;
            font-weight: 500;
            transition: all 0.2s ease;
            white-space: nowrap;
            cursor: pointer;
            border: 1px solid transparent;
            font-family: inherit;
            text-decoration: none;
            background: var(--card-bg);
            color: var(--text-secondary);
            border-color: var(--border);
        }

        .btn-primary {
            background: var(--primary);
            color: #ffffff;
            border-color: var(--primary);
        }

        .btn-primary:hover {
            background: var(--primary-hover);
            border-color: var(--primary-hover);
            color: #ffffff;
        }

        .btn-outline {
            background: var(--card-bg);
            border-color: var(--border);
            color: var(--text-secondary);
        }

        .btn-outline:hover {
            background: var(--border-light);
            border-color: var(--border);
            color: var(--text-main);
        }

        .btn-sm {
            padding: 0.15rem 0.6rem;
            font-size: 0.72rem;
            border-radius: 4px;
        }

        /* 占位卡片 */
        .placeholder-card {
            background: var(--border-light);
            border: 1px dashed var(--border);
            border-radius: var(--radius-lg);
            padding: 2rem 1.5rem;
            text-align: center;
            color: var(--text-muted);
            display: flex;
            flex-direction: column;
            align-items: center;
            gap: 0.2rem;
            animation: fadeIn 0.2s ease;
            transition: background 0.2s ease, border-color 0.2s ease, color 0.2s ease;
        }

        .placeholder-card .big-icon {
            font-size: 2rem;
            opacity: 0.5;
        }

        .placeholder-card p {
            font-size: 0.875rem;
            font-weight: 500;
            color: var(--text-muted);
        }

        /* ============================================================
           模态框
           ============================================================ */
        .modal {
            display: none;
            position: fixed;
            z-index: 1000;
            left: 0;
            top: 0;
            width: 100%;
            height: 100%;
            background-color: rgba(0, 0, 0, 0.3);
            backdrop-filter: blur(2px);
            -webkit-backdrop-filter: blur(2px);
            justify-content: center;
            align-items: center;
            transition: background-color 0.2s ease;
        }
        [data-theme="dark"] .modal {
            background-color: rgba(0, 0, 0, 0.6);
        }

        .modal.show {
            display: flex;
        }

        .modal-content {
            background: var(--card-bg);
            border-radius: var(--radius-lg);
            padding: 1.6rem 1.8rem 1.8rem;
            width: 90%;
            max-width: 660px;
            box-shadow: 0 20px 48px rgba(0, 0, 0, 0.08);
            position: relative;
            animation: modalIn 0.15s ease;
            border: 1px solid var(--border);
            transition: background 0.2s ease, border-color 0.2s ease;
        }
        [data-theme="dark"] .modal-content {
            box-shadow: 0 20px 48px rgba(0, 0, 0, 0.4);
        }

        .modal-close {
            position: absolute;
            right: 1rem;
            top: 0.6rem;
            font-size: 1.4rem;
            color: var(--text-muted);
            cursor: pointer;
            transition: color 0.2s ease;
            line-height: 1;
        }

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

        .modal-content h2 {
            font-size: 1.125rem;
            font-weight: 600;
            margin-bottom: 0.1rem;
            color: var(--text-main);
            transition: color 0.2s ease;
        }

        .modal-content .subtitle {
            color: var(--text-secondary);
            margin-bottom: 1.2rem;
            font-size: 0.85rem;
            transition: color 0.2s ease;
        }

        .version-list {
            display: flex;
            flex-direction: column;
            gap: 0.6rem;
        }

        .version-item {
            background: var(--border-light);
            border-radius: var(--radius-md);
            padding: 0.8rem 1rem;
            display: flex;
            justify-content: space-between;
            align-items: center;
            flex-wrap: wrap;
            gap: 0.6rem;
            border: 1px solid var(--border);
            transition: background 0.2s ease, border-color 0.2s ease;
        }

        .version-item:hover {
            background: var(--card-bg);
        }

        .version-info {
            flex: 1;
            min-width: 140px;
        }

        .version-info h4 {
            font-size: 0.95rem;
            font-weight: 600;
            color: var(--text-main);
            transition: color 0.2s ease;
        }

        .version-info p {
            font-size: 0.78rem;
            color: var(--text-secondary);
            margin: 0;
            transition: color 0.2s ease;
        }

        .version-actions {
            display: flex;
            gap: 0.3rem;
            align-items: center;
            flex-wrap: wrap;
        }

        .template-group {
            display: flex;
            gap: 0.2rem;
            flex-wrap: wrap;
        }

        /* ============================================================
           留言板
           ============================================================ */
        .message-board-container {
            display: flex;
            flex-direction: column;
            gap: 1.8rem;
        }

        .mailbox-form {
            background: var(--form-bg);
            border: 1px solid var(--form-border);
            border-radius: var(--radius-lg);
            padding: 1.4rem 1.6rem 1.6rem;
            position: relative;
            transition: background 0.2s ease, border-color 0.2s ease;
        }

        .mailbox-form h3 {
            font-size: 1rem;
            font-weight: 600;
            color: var(--color-message);
            margin-bottom: 0.8rem;
            display: flex;
            align-items: center;
            gap: 0.4rem;
            transition: color 0.2s ease;
        }

        .mailbox-form .form-group {
            margin-bottom: 0.8rem;
        }

        .mailbox-form label {
            display: block;
            font-weight: 500;
            margin-bottom: 0.2rem;
            font-size: 0.85rem;
            color: var(--text-secondary);
            transition: color 0.2s ease;
        }

        .mailbox-form input,
        .mailbox-form textarea {
            width: 100%;
            padding: 0.5rem 0.8rem;
            border: 1px solid var(--border);
            border-radius: var(--radius-sm);
            font-family: inherit;
            font-size: 0.875rem;
            background: var(--input-bg);
            transition: border 0.2s ease, background 0.2s ease, color 0.2s ease;
            color: var(--text-main);
        }

        .mailbox-form input:focus,
        .mailbox-form textarea:focus {
            outline: none;
            border-color: var(--color-message);
            box-shadow: 0 0 0 3px rgba(181, 123, 148, 0.12);
        }
        [data-theme="dark"] .mailbox-form input:focus,
        [data-theme="dark"] .mailbox-form textarea:focus {
            box-shadow: 0 0 0 3px rgba(217, 168, 189, 0.25);
            border-color: #d9a8bd;
        }

        .mailbox-form textarea {
            min-height: 80px;
            resize: vertical;
        }

        .mailbox-form .btn-submit {
            background: #a96480;
            color: #ffffff;
            padding: 0.4rem 1.6rem;
            font-size: 0.9rem;
            font-weight: 500;
            border: none;
            border-radius: var(--radius-sm);
            cursor: pointer;
            transition: all 0.2s ease;
        }

        .mailbox-form .btn-submit:hover {
            background: #8e5470;
        }
        [data-theme="dark"] .mailbox-form .btn-submit {
            background: #d9a8bd;
        }
        [data-theme="dark"] .mailbox-form .btn-submit:hover {
            background: #c68aa4;
        }

        .mailbox-form .btn-submit:disabled {
            opacity: 0.6;
            cursor: not-allowed;
        }

        .messages-list {
            display: flex;
            flex-direction: column;
            gap: 0.8rem;
        }

        .message-card {
            background: var(--card-bg);
            border: 1px solid var(--border);
            border-radius: var(--radius-md);
            padding: 0.9rem 1.2rem;
            transition: border 0.2s ease, background 0.2s ease;
        }

        .message-card:hover {
            border-color: var(--color-message);
        }

        .message-card .message-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 0.2rem;
        }

        .message-card .message-author {
            font-weight: 600;
            color: var(--text-main);
            font-size: 0.9rem;
            transition: color 0.2s ease;
        }

        .message-card .message-time {
            font-size: 0.72rem;
            color: var(--text-muted);
            transition: color 0.2s ease;
        }

        .message-card .message-content {
            color: var(--text-secondary);
            font-size: 0.875rem;
            line-height: 1.6;
            white-space: pre-wrap;
            transition: color 0.2s ease;
        }

        .no-messages {
            text-align: center;
            padding: 2rem;
            color: var(--text-muted);
            background: var(--border-light);
            border-radius: var(--radius-md);
            border: 1px dashed var(--border);
            font-size: 0.9rem;
            transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
        }

        .loading-messages {
            text-align: center;
            padding: 1.5rem;
            color: var(--text-muted);
            font-size: 0.875rem;
            transition: color 0.2s ease;
        }

        .error-message {
            color: #b91c1c;
            background: #fef2f2;
            padding: 0.6rem 0.8rem;
            border-radius: var(--radius-sm);
            margin-top: 0.4rem;
            font-size: 0.82rem;
            border: 1px solid #fecaca;
            transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
        }
        [data-theme="dark"] .error-message {
            color: #fca5a5;
            background: rgba(127, 29, 29, 0.4);
            border-color: #7f1d1d;
        }

        .success-message {
            color: #065f46;
            background: #ecfdf5;
            padding: 0.6rem 0.8rem;
            border-radius: var(--radius-sm);
            margin-top: 0.4rem;
            font-size: 0.82rem;
            border: 1px solid #a7f3d0;
            transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
        }
        [data-theme="dark"] .success-message {
            color: #6ee7b7;
            background: rgba(6, 78, 59, 0.4);
            border-color: #065f46;
        }

        /* ============================================================
           页脚
           ============================================================ */
        .footer-disclaimer {
            text-align: center;
            font-size: 0.78rem;
            color: var(--text-muted);
            padding: 1rem 1.5rem 0.5rem;
            line-height: 1.6;
            max-width: 800px;
            margin: 0 auto;
            transition: color 0.2s ease;
        }

        /* 底部footer已注释掉，保留占位 */

        /* ============================================================
           响应式适配
           ============================================================ */
        /* 全局兜底：杜绝意外横向滚动 */
        html,
        body {
            overflow-x: hidden;
        }

        @media (max-width: 900px) {
            .container {
                flex-direction: column;
                gap: 1rem;
                padding: 1rem 0.8rem;
            }

            .sidebar {
                width: 100%;
                position: static;
                padding: 0.6rem 0.4rem;
                border-radius: var(--radius-md);
                overflow-x: auto;
                -webkit-overflow-scrolling: touch;
            }

            .sidebar-nav {
                flex-direction: row;
                flex-wrap: nowrap;
                gap: 0.1rem;
                justify-content: flex-start;
            }

            .sidebar-nav .nav-item {
                padding: 0.4rem 0.8rem;
                font-size: 0.8rem;
                border-radius: var(--radius-sm);
                flex-shrink: 0;
                border: 1px solid transparent;
            }

            .sidebar-nav .nav-item.active {
                background: var(--primary-light);
                border-color: var(--primary-border);
            }

            .sidebar-nav .nav-item.active::before {
                display: none;
            }

            .nav-icon {
                width: 1.2rem;
            }

            .nav-icon svg {
                width: 1.2rem;
                height: 1.2rem;
            }

            .nav-item.category-others .nav-icon svg {
                width: 1.05rem;
                height: 1.05rem;
            }

            .panel-header .panel-icon svg {
                width: 1.6rem;
                height: 1.6rem;
            }

            .navbar {
                padding: 0.5rem 1rem;
            }

            .navbar-logo {
                font-size: 1.25rem;
            }

            .navbar-meta {
                font-size: 0.75rem;
                gap: 0.3rem 0.8rem;
            }

            .visit-number {
                font-size: 1rem;
            }

            .hero h1 {
                font-size: 1.2rem;
            }

            .hero p {
                font-size: 0.8rem;
            }

            .tool-grid {
                grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
            }

            .panel-header h2 {
                font-size: 1rem;
            }

            .modal-content {
                padding: 1.2rem;
            }

            .version-item {
                flex-direction: column;
                align-items: stretch;
            }

            .version-actions {
                justify-content: flex-start;
            }

            .mailbox-form {
                padding: 1rem;
            }

            .subject-tabs {
                overflow-x: auto;
                flex-wrap: nowrap;
                -webkit-overflow-scrolling: touch;
            }

            .subject-tab {
                padding: 0.3rem 0.9rem;
                font-size: 0.75rem;
                flex-shrink: 0;
                border-right: 1px solid var(--border);
            }
        }

        /* ============================================================
           手机竖屏（≤600px）适配
           ============================================================ */
        @media (max-width: 600px) {
            /* 顶栏：允许换行，徽章不再撑破布局 */
            .navbar {
                flex-wrap: wrap;
                padding: 0.5rem 0.8rem;
            }

            .navbar-meta {
                flex-wrap: wrap;
                gap: 0.3rem 0.6rem;
            }

            .navbar-logo {
                font-size: 1.15rem;
            }

            /* 超长联系徽章收缩为省略号 */
            .contact-badge {
                max-width: 42vw;
                overflow: hidden;
                text-overflow: ellipsis;
                white-space: nowrap;
            }

            .visit-count-badge {
                font-size: 0.72rem;
            }

            /* Hero 收窄 */
            .hero {
                padding: 1.3rem 1rem 1.1rem;
            }

            .hero h1 {
                font-size: 1.1rem;
            }

            .hero p {
                font-size: 0.78rem;
            }

            .container {
                padding: 0.9rem 0.7rem;
            }

            /* 侧边栏分类：胶囊自动换行 */
            .sidebar-nav {
                flex-wrap: wrap;
                gap: 0.35rem;
            }

            .sidebar-nav .nav-item {
                padding: 0.45rem 0.9rem;
            }

            .tool-card {
                padding: 0.9rem 1rem;
            }

            .modal-content {
                width: 94%;
                padding: 1.2rem 1.1rem;
            }
        }

        @media (max-width: 480px) {
            .navbar-logo {
                font-size: 1.05rem;
            }

            .navbar-meta .update-badge,
            .navbar-meta .contact-badge {
                font-size: 0.7rem;
                padding: 0.1rem 0.6rem;
            }

            .visit-number {
                font-size: 0.9rem;
            }

            .hero {
                padding: 1.2rem 1rem;
            }

            .hero h1 {
                font-size: 1rem;
            }

            .tool-card {
                padding: 0.8rem 1rem;
            }

            .tool-card h3 {
                font-size: 0.9rem;
            }

            .modal-content {
                padding: 1rem;
            }
        }
    
/* ============================================================
   视觉优化（2026-08-23）
   说明：本块为追加的覆盖样式，如不满意可整体删除回滚。
   ============================================================ */

/* ① 顶部导航栏：毛玻璃 */
.navbar {
    background: rgba(255, 255, 255, 0.82);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    box-shadow: 0 1px 0 rgba(0, 0, 0, 0.03);
}
[data-theme="dark"] .navbar {
    background: rgba(15, 23, 42, 0.82);
}

/* ② Logo 渐变色（品牌感） */
.navbar-logo {
    background: linear-gradient(135deg, #1e3a8a 0%, #1d4ed8 55%, #0ea5e9 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    color: transparent;
    letter-spacing: 0.02em;
}
[data-theme="dark"] .navbar-logo {
    background: linear-gradient(135deg, #60a5fa 0%, #38bdf8 55%, #2dd4bf 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

/* ④ Hero 渐变背景 + 装饰圆 */
.hero {
    background: linear-gradient(135deg, #eff6ff 0%, #dbeafe 45%, #f0f9ff 100%);
    position: relative;
    overflow: hidden;
}
[data-theme="dark"] .hero {
    background: linear-gradient(135deg, #0f172a 0%, #1e1b4b 50%, #172554 100%);
}
.hero::before,
.hero::after {
    content: "";
    position: absolute;
    border-radius: 50%;
    background: radial-gradient(circle, rgba(37, 99, 235, 0.14), transparent 70%);
    pointer-events: none;
    z-index: 0;
}
.hero::before {
    width: 280px;
    height: 280px;
    top: -90px;
    left: -70px;
}
.hero::after {
    width: 340px;
    height: 340px;
    bottom: -130px;
    right: -90px;
    background: radial-gradient(circle, rgba(14, 165, 233, 0.12), transparent 70%);
}
.hero h1,
.hero p {
    position: relative;
    z-index: 1;
}

/* ⑥ Hero 标题渐变色文字 */
.hero h1 {
    background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 60%, #0ea5e9 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
    color: transparent;
}
[data-theme="dark"] .hero h1 {
    background: linear-gradient(135deg, #bfdbfe 0%, #60a5fa 60%, #22d3ee 100%);
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

/* ⑦ 侧边栏选中项：分类色浅底块 */
.sidebar-nav .nav-item.category-physics.active {
    background: rgba(192, 138, 94, 0.12);
}
.sidebar-nav .nav-item.category-others.active {
    background: rgba(155, 140, 192, 0.12);
}
.sidebar-nav .nav-item.category-public.active {
    background: rgba(127, 179, 172, 0.12);
}
.sidebar-nav .nav-item.category-class.active {
    background: rgba(127, 168, 196, 0.12);
}
.sidebar-nav .nav-item.category-analysis.active {
    background: rgba(134, 181, 152, 0.12);
}
.sidebar-nav .nav-item.category-message.active {
    background: rgba(181, 123, 148, 0.12);
}

/* ⑨ 工具卡片：分类彩色顶边 */
.tool-card::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    border-radius: var(--radius-lg) var(--radius-lg) 0 0;
    background: var(--color-public);
}
#panel-physics .tool-card::before {
    background: var(--color-physics);
}
#panel-other-subjects .tool-card::before {
    background: var(--color-others);
}
#panel-public-lesson .tool-card::before {
    background: var(--color-public);
}
#panel-class-mgmt .tool-card::before {
    background: var(--color-class);
}
#panel-analysis .tool-card::before {
    background: var(--color-analysis);
}

/* ⑪ 卡片 hover 提升 */
.tool-card:hover {
    transform: translateY(-4px);
    box-shadow: 0 10px 24px rgba(0, 0, 0, 0.10);
    border-color: var(--primary-border);
}

/* ⑫ 卡片交错进入动画 */
.tool-card {
    animation: cardIn 0.45s ease both;
}
@keyframes cardIn {
    from {
        opacity: 0;
        transform: translateY(14px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}
.tool-card:nth-child(1) { animation-delay: 0.04s; }
.tool-card:nth-child(2) { animation-delay: 0.10s; }
.tool-card:nth-child(3) { animation-delay: 0.16s; }
.tool-card:nth-child(4) { animation-delay: 0.22s; }
.tool-card:nth-child(5) { animation-delay: 0.28s; }

/* ⑬ 按钮悬停微交互 */
.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: 0 5px 12px rgba(0, 0, 0, 0.16);
}

/* ⑰ 占位卡片美化 */
.placeholder-card {
    background: linear-gradient(135deg, var(--border-light), var(--card-bg));
    border-style: dashed;
}
.placeholder-card .big-icon {
    font-size: 2.4rem;
    opacity: 0.6;
}

/* ⑱ 自定义滚动条 */
::-webkit-scrollbar {
    width: 10px;
    height: 10px;
}
::-webkit-scrollbar-track {
    background: transparent;
}
::-webkit-scrollbar-thumb {
    background: var(--border);
    border-radius: 6px;
}
::-webkit-scrollbar-thumb:hover {
    background: var(--text-muted);
}

/* ⑲ 文本选中色 */
::selection {
    background: var(--primary);
    color: #ffffff;
}

/* ⑳ 主题切换过渡强化 */
.navbar,
.sidebar,
.tool-card,
.tool-meta span,
.subject-tab,
.message-card,
.mailbox-form,
.version-item {
    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease, box-shadow 0.2s ease;
}