/* ============ 设计变量 ============ */
        :root {
            --primary: #2563eb;
            --primary-deep: #1d4ed8;
            --primary-soft: #dbeafe;
            --accent: #ea580c;
            --accent-soft: #ffedd5;
            --success: #059669;
            --success-soft: #d1fae5;
            --danger: #dc2626;
            --danger-soft: #fee2e2;
            --warning: #d97706;
            --warning-soft: #fef3c7;
            --info: #7c3aed;
            --info-soft: #ede9fe;
            --ink: #0f172a;
            --ink-2: #334155;
            --ink-3: #64748b;
            --line: #e2e8f0;
            --controls-safe-height: 52px;
            --heading-font: 'JF Open Hun Inn', 'Microsoft YaHei', 'Segoe UI', sans-serif;
            --handwriting-font: 'JF Open Hun Inn', 'Microsoft YaHei', 'Segoe UI', sans-serif;
            /* 兼容旧变量名（可视化脚本仍会引用） */
            --primary-color: #2563eb;
            --accent-color: #ea580c;
            --success-color: #059669;
            --danger-color: #dc2626;
            --warning-color: #d97706;
            --info-color: #7c3aed;
            --text-color: #334155;
        }

        * { box-sizing: border-box; }

        body {
            font-family: var(--heading-font);
            background: #eef2f9;
            overflow: hidden;
            margin: 0;
            color: var(--ink-2);
            min-height: 100vh;
        }

        #presentation-container {
            width: 100%;
            height: 100vh;
            max-width: 100vw;
            position: relative;
            background: #ffffff;
            box-sizing: border-box;
            overflow: hidden;
        }

        /* ============ 幻灯片 ============ */
        .slide {
            width: 100%;
            height: 100%;
            display: none;
            opacity: 0;
            visibility: hidden;
            align-items: stretch;
        }
        .slide.active {
            display: flex;
            opacity: 1;
            visibility: visible;
            animation: fadeIn 0.5s ease-in-out;
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(14px); }
            to   { opacity: 1; transform: translateY(0); }
        }
        @keyframes fadeInUp {
            from { opacity: 0; transform: translateY(28px); }
            to   { opacity: 1; transform: translateY(0); }
        }
        @keyframes popIn {
            from { opacity: 0; transform: scale(.96) translateY(8px); }
            to   { opacity: 1; transform: scale(1) translateY(0); }
        }
        @keyframes floatY {
            0%, 100% { transform: translateY(0); }
            50%      { transform: translateY(-12px); }
        }
        @keyframes spin  { to { transform: rotate(360deg); } }
        @keyframes spinR { to { transform: rotate(-360deg); } }

        @media (prefers-reduced-motion: reduce) {
            .slide.active, .concept-card, .cover-center, .math-badge, .orbit { animation: none !important; }
        }

        /* ============ 左侧讲解区 ============ */
        .chalkboard {
            width: 50%;
            height: 100%;
            background: linear-gradient(180deg, #ffffff, #fafcff);
            color: var(--ink-2);
            padding: 36px 46px calc(28px + var(--controls-safe-height));
            display: flex;
            flex-direction: column;
            justify-content: flex-start;
            overflow-y: auto;
            box-sizing: border-box;
            line-height: 1.85;
            font-size: 16.5px;
            border-right: 1px solid var(--line);
        }
        .chalkboard::-webkit-scrollbar { width: 8px; }
        .chalkboard::-webkit-scrollbar-thumb { background: #cbd5e1; border-radius: 8px; }
        .chalkboard::-webkit-scrollbar-track { background: transparent; }

        .slide-kicker {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            font-size: 13px;
            font-weight: 700;
            color: var(--ink-3);
            letter-spacing: .14em;
            margin-bottom: 4px;
        }
        .kicker-num {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            min-width: 28px;
            height: 20px;
            padding: 0 7px;
            border-radius: 6px;
            background: var(--primary-soft);
            color: var(--primary-deep);
            font-size: 12px;
            letter-spacing: 0;
        }

        .chalkboard h2 {
            display: flex;
            align-items: center;
            gap: 12px;
            font-size: 27px;
            color: var(--ink);
            margin: 4px 0 10px;
            padding-bottom: 14px;
            position: relative;
        }
        .chalkboard h2::after {
            content: '';
            position: absolute;
            left: 0;
            bottom: 0;
            width: 78px;
            height: 4px;
            border-radius: 99px;
            background: linear-gradient(90deg, var(--primary), var(--info), var(--accent));
        }
        .h-icon {
            width: 38px;
            height: 38px;
            flex: 0 0 38px;
            border-radius: 11px;
            display: flex;
            align-items: center;
            justify-content: center;
            color: #fff;
            font-size: 16px;
            background: var(--hc, var(--primary));
            box-shadow: 0 6px 14px rgba(15, 23, 42, .18);
        }

        .chalkboard h3 { font-size: 19px; color: var(--ink); margin: 0; }
        .chalkboard h4 { font-size: 17px; color: var(--ink-2); margin: 16px 0 8px; }
        .chalkboard p  { margin: 10px 0; }
        .lead { font-size: 17px; color: var(--ink-2); }

        .chalkboard ul { padding-left: 22px; margin: 10px 0; }
        .chalkboard ol { padding-left: 24px; }
        .chalkboard li { margin-bottom: 8px; }

        .highlight {
            color: var(--accent);
            font-weight: 700;
            background: linear-gradient(transparent 64%, var(--accent-soft) 0);
            padding: 0 3px;
            border-radius: 3px;
        }

        /* 知识卡片 */
        .concept-card {
            position: relative;
            background: #fff;
            border: 1px solid var(--line);
            border-left: 4px solid var(--cc, var(--primary));
            border-radius: 14px;
            padding: 13px 18px 14px;
            margin: 14px 0;
            box-shadow: 0 4px 14px rgba(15, 23, 42, .05);
            animation: popIn .5s ease both;
        }
        .concept-card:nth-of-type(2) { animation-delay: .08s; }
        .concept-card:nth-of-type(3) { animation-delay: .16s; }
        .card-head { display: flex; align-items: center; gap: 10px; margin-bottom: 5px; }
        .card-icon {
            width: 30px;
            height: 30px;
            flex: 0 0 30px;
            border-radius: 9px;
            display: flex;
            align-items: center;
            justify-content: center;
            color: #fff;
            font-size: 13px;
            background: var(--cc, var(--primary));
        }
        .concept-card p { margin: 6px 0; }

        /* 例题 / 提示 */
        .example {
            display: block;
            background: #f8fafc;
            border: 1px dashed #d8e2ef;
            border-radius: 10px;
            padding: 9px 14px;
            margin-top: 10px;
            font-size: 15px;
            color: var(--ink-2);
        }
        .example .fa-solid { color: var(--ink-3); margin-right: 6px; font-size: 13px; }
        .ex-block { margin: 10px 0; }

        .tip-box {
            display: flex;
            gap: 10px;
            align-items: flex-start;
            background: #fffbeb;
            border: 1px solid #fde68a;
            border-radius: 12px;
            padding: 11px 14px;
            margin: 16px 0 6px;
            color: #92400e;
            font-size: 15px;
            line-height: 1.7;
        }
        .tip-icon { font-size: 17px; line-height: 1.5; flex: 0 0 auto; }

        /* 公式框 */
        .math-formula {
            background: linear-gradient(135deg, #eff6ff, #f5f3ff);
            border: 1px solid #dbeafe;
            border-radius: 14px;
            padding: 14px 20px;
            margin: 16px 0;
            text-align: center;
            font-size: 1.25rem;
            color: #1e3a8a;
            line-height: 1.6;
            box-shadow: inset 0 1px 0 #fff, 0 4px 14px rgba(37, 99, 235, .08);
        }

        /* 输入/法则/输出 三枚小卡 */
        .io-chips { display: flex; gap: 10px; margin: 14px 0; flex-wrap: wrap; }
        .io-chip {
            flex: 1;
            min-width: 118px;
            background: #fff;
            border: 1px solid var(--line);
            border-top: 3px solid var(--cc, var(--primary));
            border-radius: 12px;
            padding: 10px 12px;
            text-align: center;
            box-shadow: 0 4px 12px rgba(15, 23, 42, .05);
        }
        .io-chip b { display: block; font-size: 19px; color: var(--cc, var(--primary)); }
        .io-chip span { font-size: 13px; color: var(--ink-3); }

        /* 区间四宫格 */
        .interval-grid {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 12px;
            margin: 14px 0;
        }
        .interval-card {
            background: #fff;
            border: 1px solid var(--line);
            border-top: 3px solid var(--cc, var(--primary));
            border-radius: 14px;
            padding: 12px 14px;
            text-align: center;
            box-shadow: 0 4px 12px rgba(15, 23, 42, .05);
        }
        .iv-nota { font-size: 20px; font-weight: 800; color: var(--cc, var(--primary)); }
        .iv-name { font-size: 14px; color: var(--ink); font-weight: 700; margin: 2px 0; }
        .iv-ineq { font-size: 13.5px; color: var(--ink-3); }

        /* 勾选式规则列表 */
        ul.rules { list-style: none; padding: 0; margin: 12px 0; }
        ul.rules li {
            position: relative;
            padding: 8px 12px 8px 40px;
            margin: 8px 0;
            background: #fff;
            border: 1px solid var(--line);
            border-radius: 10px;
            box-shadow: 0 3px 10px rgba(15, 23, 42, .04);
        }
        ul.rules li::before {
            content: '✓';
            position: absolute;
            left: 11px;
            top: 50%;
            transform: translateY(-50%);
            width: 20px;
            height: 20px;
            border-radius: 50%;
            background: var(--success);
            color: #fff;
            font-size: 11px;
            display: flex;
            align-items: center;
            justify-content: center;
        }

        /* MathJax 兼容 */
        .chalkboard mjx-container { max-width: 100%; }
        .chalkboard mjx-container[display="true"] {
            display: block;
            text-align: center !important;
            margin: 6px 0;
        }

        /* ============ 右侧可视化区 ============ */
        .visualization {
            width: 50%;
            height: 100%;
            position: relative;
            padding: 26px;
            padding-bottom: calc(26px + var(--controls-safe-height));
            display: flex;
            align-items: center;
            justify-content: center;
            border-left: 1px solid #e6ecf5;
            overflow: hidden;
            background:
                radial-gradient(circle at 1px 1px, rgba(37, 99, 235, .09) 1px, transparent 1.6px) 0 0 / 24px 24px,
                linear-gradient(180deg, #fbfdff, #f3f8ff);
        }
        .visualization svg {
            display: block;
            width: 100%;
            height: 100%;
            max-width: 100%;
            max-height: 100%;
            font-family: var(--heading-font);
        }
        .visualization canvas { max-width: 100%; max-height: 100%; }
        .visualization.full-width { width: 100%; border-left: none; }

        /* ============ 封面 ============ */
        .slide-container { width: 100%; height: 100%; display: flex; }
        .slide-container.cover {
            align-items: stretch;
            background: linear-gradient(145deg, #fffdf7 0%, #f6faff 45%, #edf3ff 100%);
        }
        .cover-left {
            width: 52%;
            padding: 54px 60px calc(54px + var(--controls-safe-height));
            display: flex;
            flex-direction: column;
            justify-content: center;
        }
        .cover-right { width: 48%; position: relative; overflow: hidden; }

        .cover-badge {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            border: 1px solid #bfdbfe;
            background: #eff6ff;
            color: #1d4ed8;
            padding: 6px 14px;
            border-radius: 999px;
            font-size: 15px;
            font-weight: 800;
            width: fit-content;
        }
        .cover-title {
            font-size: 56px;
            line-height: 1.1;
            margin: 18px 0 12px;
            color: #1e3a8a;
            background: linear-gradient(92deg, #1e3a8a 0%, #2563eb 55%, #c2410c 100%);
            -webkit-background-clip: text;
            background-clip: text;
            -webkit-text-fill-color: transparent;
            animation: fadeInUp .7s ease both;
        }
        .cover-subtitle {
            font-size: 19px;
            color: #475569;
            margin: 0 0 18px;
            line-height: 1.8;
            animation: fadeInUp .7s .1s ease both;
        }
        .cover-meta {
            display: flex;
            gap: 12px;
            flex-wrap: wrap;
            color: #64748b;
            font-size: 15px;
            animation: fadeInUp .7s .18s ease both;
        }
        .cover-meta span {
            display: inline-flex;
            align-items: center;
            gap: 7px;
            background: #fff;
            border: 1px solid var(--line);
            padding: 6px 13px;
            border-radius: 999px;
            box-shadow: 0 2px 8px rgba(15, 23, 42, .05);
        }
        .cover-meta .fa-solid { color: var(--primary); font-size: 13px; }
        .cover-actions {
            display: flex;
            gap: 12px;
            margin-top: 26px;
            flex-wrap: wrap;
            animation: fadeInUp .7s .26s ease both;
        }
        .start-btn {
            display: inline-flex;
            align-items: center;
            gap: 9px;
            min-height: 42px;
            padding: 0 22px;
            border: none;
            border-radius: 12px;
            background: linear-gradient(135deg, #2563eb, #7c3aed);
            color: #fff;
            font-size: 16px;
            font-weight: 800;
            font-family: inherit;
            cursor: pointer;
            box-shadow: 0 10px 24px rgba(37, 99, 235, .35);
            transition: transform .2s ease, box-shadow .2s ease;
        }
        .start-btn:hover { transform: translateY(-2px); box-shadow: 0 14px 30px rgba(37, 99, 235, .42); }
        .home-link-btn {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            justify-content: center;
            min-height: 42px;
            padding: 0 18px;
            border: 1px solid #cbd5e1;
            border-radius: 12px;
            background: #ffffff;
            color: #334155;
            font-size: 15px;
            font-weight: 700;
            text-decoration: none;
            box-shadow: 0 2px 8px rgba(15, 23, 42, .06);
            transition: all .2s ease;
        }
        .home-link-btn:hover { border-color: #60a5fa; color: #1d4ed8; background: #eff6ff; }
        .cover-hint { margin-top: 18px; font-size: 13px; color: #94a3b8; animation: fadeInUp .7s .34s ease both; }

        .cover-visual {
            position: relative;
            width: 100%;
            height: 100%;
            background:
                radial-gradient(720px 540px at 74% 26%, rgba(37, 99, 235, .14), transparent 62%),
                radial-gradient(680px 520px at 22% 76%, rgba(234, 88, 12, .12), transparent 64%);
        }
        .cover-visual::after {
            content: '';
            position: absolute;
            inset: 0;
            background: radial-gradient(560px 260px at 50% -10%, rgba(255, 255, 255, .55), transparent 72%);
            pointer-events: none;
        }
        .cover-center {
            position: absolute;
            left: 50%;
            top: 50%;
            transform: translate(-50%, -50%);
            width: 116px;
            height: 116px;
            border-radius: 30px;
            background: linear-gradient(135deg, #2563eb, #7c3aed);
            display: flex;
            align-items: center;
            justify-content: center;
            color: #fff;
            font-size: 54px;
            font-style: italic;
            font-weight: 800;
            box-shadow: 0 20px 44px rgba(37, 99, 235, .38);
            z-index: 2;
        }
        .orbit {
            position: absolute;
            left: 50%;
            top: 50%;
            width: 330px;
            height: 330px;
            margin: -165px 0 0 -165px;
            border-radius: 50%;
            border: 1.5px dashed rgba(37, 99, 235, .35);
            animation: spin 20s linear infinite;
        }
        .orbit .dot {
            position: absolute;
            top: -7px;
            left: 50%;
            width: 14px;
            height: 14px;
            margin-left: -7px;
            border-radius: 50%;
            background: #2563eb;
            box-shadow: 0 0 0 6px rgba(37, 99, 235, .15);
        }
        .orbit.orbit-2 {
            width: 214px;
            height: 214px;
            margin: -107px 0 0 -107px;
            border-color: rgba(234, 88, 12, .35);
            animation: spinR 14s linear infinite;
        }
        .orbit-2 .dot { background: #ea580c; box-shadow: 0 0 0 6px rgba(234, 88, 12, .15); }
        .math-badge {
            position: absolute;
            padding: 8px 13px;
            background: rgba(255, 255, 255, .86);
            border: 1px solid rgba(148, 163, 184, .28);
            border-radius: 10px;
            box-shadow: 0 10px 22px rgba(15, 23, 42, .10);
            color: #334155;
            font-weight: 800;
            font-size: 15px;
            animation: floatY 6s ease-in-out infinite;
            backdrop-filter: blur(4px);
            z-index: 3;
        }
        .math-badge.b1 { left: 10%; top: 18%; }
        .math-badge.b2 { right: 9%; top: 28%; animation-delay: .9s; }
        .math-badge.b3 { left: 15%; bottom: 20%; animation-delay: 1.6s; }
        .math-badge.b4 { right: 13%; bottom: 14%; animation-delay: 2.3s; }

        /* ============ 底部控制栏 ============ */
        .controls {
            position: fixed;
            left: 0;
            bottom: 0;
            width: 100vw;
            height: var(--controls-safe-height);
            display: flex;
            flex-direction: row;
            justify-content: center;
            align-items: center;
            gap: 1.05rem;
            z-index: 1000;
            background: rgba(255, 255, 255, .93);
            border-top: 1px solid var(--line);
            box-shadow: 0 -6px 20px rgba(15, 23, 42, .07);
            backdrop-filter: blur(8px);
            padding: 0 1rem;
        }
        .controls .nav-btn {
            width: auto;
            height: auto;
            border: none;
            background: transparent;
            color: #475569;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            gap: .45rem;
            padding: .34rem .55rem;
            border-radius: 8px;
            font-size: .93rem;
            font-weight: 700;
            font-family: inherit;
            transition: color .18s ease, background .18s ease, transform .18s ease;
        }
        .controls .nav-btn:hover { color: var(--primary); background: var(--primary-soft); }
        .controls .nav-btn.at-first,
        .controls .nav-btn.at-last { opacity: .45; }
        .page-indicator {
            min-width: 88px;
            color: var(--primary-deep);
            background: var(--primary-soft);
            border-radius: 999px;
            padding: 4px 13px;
            font-weight: 800;
            text-align: center;
            font-size: .98rem;
        }
        .page-jump {
            display: flex;
            align-items: center;
            gap: .4rem;
            color: #475569;
            font-size: .88rem;
            white-space: nowrap;
        }
        .page-jump-input {
            width: 4rem;
            height: 1.9rem;
            border: 1px solid #cbd5e1;
            border-radius: .5rem;
            text-align: center;
            font-weight: 700;
            font-family: inherit;
            color: #0f172a;
            background: #fff;
        }
        .page-jump-input:focus { outline: 2px solid #93c5fd; border-color: #60a5fa; }
        .page-jump-btn {
            height: 1.9rem;
            padding: 0 .6rem;
            border: 1px solid #cbd5e1;
            border-radius: .5rem;
            background: #f8fafc;
            color: #334155;
            font-size: .84rem;
            font-weight: 700;
            font-family: inherit;
            cursor: pointer;
            transition: all .18s ease;
        }
        .page-jump-btn:hover { border-color: #60a5fa; color: #1d4ed8; background: #eff6ff; }

        .progress-bar-container {
            position: fixed;
            top: 0;
            left: 0;
            width: 100%;
            height: 4px;
            background: transparent;
            z-index: 1000;
        }
        .progress-bar {
            height: 100%;
            width: 0%;
            background: linear-gradient(90deg, #2563eb, #7c3aed, #ea580c);
            border-radius: 0 99px 99px 0;
            transition: width .3s ease-out;
        }

        /* ============ 二级菜单（目录 / 实验室） ============ */
        .lab-submenu {
            position: fixed;
            top: 11%;
            left: 50%;
            transform: translateX(-50%);
            z-index: 1100;
            width: min(96%, 980px);
            max-height: 78vh;
            overflow-y: auto;
            overflow-x: hidden;
            background: rgba(255, 255, 255, .97);
            border-radius: 18px;
            box-shadow: 0 24px 70px rgba(15, 23, 42, .28);
            backdrop-filter: blur(16px);
            border: 1px solid #eef2f7;
        }
        .submenu-content { padding: 26px; position: relative; }
        .submenu-title {
            text-align: center;
            font-size: 22px;
            font-weight: bold;
            color: var(--ink);
            margin-bottom: 18px;
            padding-bottom: 12px;
            border-bottom: 2px solid var(--primary-soft);
        }
        .submenu-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(208px, 1fr));
            gap: 12px;
            max-height: 60vh;
            overflow-y: auto;
        }
        .submenu-item {
            display: flex;
            align-items: center;
            padding: 12px 15px;
            background: #f8fafc;
            border: 1px solid transparent;
            border-radius: 12px;
            cursor: pointer;
            transition: all .25s ease;
            font-size: 14px;
            color: var(--ink);
        }
        .submenu-item:hover {
            background: linear-gradient(135deg, var(--primary), var(--info));
            color: #fff;
            transform: translateY(-2px);
            box-shadow: 0 8px 18px rgba(37, 99, 235, .3);
        }
        .submenu-icon { margin-right: 10px; font-size: 15px; color: var(--primary); transition: color .25s ease; }
        .submenu-item:hover .submenu-icon { color: #fff; }
        .submenu-text { font-weight: 600; }
        .submenu-close {
            position: absolute;
            top: 12px;
            right: 16px;
            width: 28px;
            height: 28px;
            background: var(--danger);
            color: white;
            border: none;
            border-radius: 50%;
            cursor: pointer;
            display: flex;
            align-items: center;
            justify-content: center;
            font-size: 16px;
            font-weight: bold;
            transition: all .25s ease;
        }
        .submenu-close:hover { background: #b91c1c; transform: scale(1.1); }

        /* ============ 响应式：平板 ============ */
        @media (max-width: 960px) {
            :root { --controls-safe-height: 92px; }

            #presentation-container {
                height: 100dvh;
                min-height: 100dvh;
                padding-bottom: calc(var(--controls-safe-height) + env(safe-area-inset-bottom, 0px));
            }
            .slide { flex-direction: column; min-height: 0; height: 100%; }
            .slide.active { min-height: 0; animation: none; transform: none; }

            .chalkboard {
                width: 100%;
                flex: 1 1 auto;
                min-height: 0;
                height: auto;
                padding: 20px 18px 24px;
                font-size: 14px;
                line-height: 1.7;
                border-right: none;
                border-bottom: 1px solid var(--line);
                overflow-y: auto;
                overscroll-behavior: contain;
            }
            .visualization {
                width: 100%;
                flex: 0 0 clamp(220px, 32vh, 310px);
                min-height: clamp(220px, 32vh, 310px);
                height: auto;
                padding: 14px;
                padding-bottom: 14px;
                border-left: none;
                border-top: 1px solid #e6ecf5;
            }

            .chalkboard h2 { font-size: 19px; margin-bottom: 8px; padding-bottom: 10px; gap: 9px; }
            .h-icon { width: 30px; height: 30px; flex-basis: 30px; border-radius: 9px; font-size: 13px; }
            .chalkboard h3 { font-size: 16px; }
            .chalkboard h4 { font-size: 14px; margin: 12px 0 8px; }
            .chalkboard p, .chalkboard li { font-size: 13px; margin-bottom: 8px; }
            .lead { font-size: 13.5px; }
            .slide-kicker { font-size: 11.5px; }
            .math-formula { padding: 11px 14px; margin: 12px 0; font-size: 1rem; }
            .concept-card { padding: 11px 14px; margin: 11px 0; border-radius: 12px; }
            .card-icon { width: 26px; height: 26px; flex-basis: 26px; font-size: 11.5px; }
            .example { font-size: 12.5px; padding: 8px 11px; }
            .tip-box { font-size: 12.5px; padding: 9px 12px; margin: 12px 0 4px; }
            .io-chip { min-width: 96px; padding: 8px 9px; }
            .io-chip b { font-size: 16px; }
            .io-chip span { font-size: 11.5px; }
            .interval-grid { gap: 9px; margin: 11px 0; }
            .interval-card { padding: 9px 10px; }
            .iv-nota { font-size: 17px; }
            .iv-name { font-size: 12.5px; }
            .iv-ineq { font-size: 12px; }
            ul.rules li { padding: 7px 10px 7px 36px; margin: 7px 0; }

            .slide-container { flex-direction: column; min-height: 0; height: 100%; }
            .slide-container.cover { display: flex; flex-direction: column-reverse; height: 100%; min-height: 100%; }
            .cover-left {
                width: 100%;
                padding: 16px 22px calc(16px + var(--controls-safe-height));
                justify-content: flex-start;
                overflow-y: auto;
            }
            .cover-right { width: 100%; flex: 0 0 auto; }
            .cover-visual { height: 218px; }
            .cover-title { font-size: 36px; margin: 12px 0 8px; }
            .cover-subtitle { font-size: 15px; margin-bottom: 12px; }
            .cover-badge { font-size: 13px; padding: 5px 11px; }
            .cover-meta { gap: 8px; font-size: 12.5px; }
            .cover-meta span { padding: 4px 10px; }
            .cover-actions { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 9px; margin-top: 16px; }
            .start-btn { min-height: 40px; font-size: 15px; padding: 0 10px; }
            .home-link-btn { min-height: 40px; font-size: 14px; padding: 0 10px; }
            .cover-hint { font-size: 12px; margin-top: 12px; }
            .orbit { width: 196px; height: 196px; margin: -98px 0 0 -98px; }
            .orbit.orbit-2 { width: 128px; height: 128px; margin: -64px 0 0 -64px; }
            .cover-center { width: 82px; height: 82px; font-size: 38px; border-radius: 22px; }
            .math-badge { font-size: 12px; padding: 5px 9px; }

            .controls {
                display: flex;
                justify-content: flex-start;
                align-items: center;
                gap: .7rem;
                min-height: 56px;
                height: auto;
                padding: .5rem .85rem calc(.5rem + env(safe-area-inset-bottom, 0px));
                overflow-x: auto;
                overflow-y: hidden;
            }
            .controls .nav-btn { flex: 0 0 auto; min-width: max-content; gap: .32rem; font-size: .85rem; }
            .controls .nav-ico { font-size: 1rem; line-height: 1; }
            .page-indicator { flex: 0 0 auto; min-width: 70px; font-size: .9rem; padding: 3px 10px; }
            .page-jump { flex: 0 0 auto; gap: .3rem; justify-content: flex-start; }
            .page-jump-input { width: 3.2rem; height: 34px; }
            .page-jump-btn { height: 34px; padding: 0 .45rem; font-size: .78rem; }

            .lab-submenu { width: 94%; max-height: 75vh; }
            .submenu-content { padding: 16px; }
        }

        /* ============ 响应式：手机 ============ */
        @media (max-width: 560px) {
            :root { --controls-safe-height: 86px; }
            body { font-size: 12px; }

            .chalkboard { padding: 15px 13px 20px; font-size: 12.5px; line-height: 1.55; }
            .visualization {
                flex-basis: clamp(200px, 27vh, 250px);
                min-height: clamp(200px, 27vh, 250px);
                padding: 10px;
            }
            .chalkboard h2 { font-size: 16.5px; margin-bottom: 8px; padding-bottom: 8px; }
            .chalkboard h3 { font-size: 14px; }
            .chalkboard p, .chalkboard li { font-size: 12px; margin-bottom: 6px; line-height: 1.5; }
            .chalkboard ul, .chalkboard ol { padding-left: 16px; margin: 8px 0; }
            .math-formula { padding: 9px; margin: 10px 0; font-size: .9rem; border-radius: 10px; }
            .interval-grid { gap: 7px; }
            .iv-nota { font-size: 15px; }

            .cover-title { font-size: 30px; }
            .cover-visual { height: 186px; }
            .orbit { width: 164px; height: 164px; margin: -82px 0 0 -82px; }
            .orbit.orbit-2 { width: 106px; height: 106px; margin: -53px 0 0 -53px; }
            .cover-center { width: 70px; height: 70px; font-size: 32px; border-radius: 19px; }

            .controls { gap: .48rem; min-height: 52px; padding: .48rem .7rem calc(.48rem + env(safe-area-inset-bottom, 0px)); }
            .controls .nav-btn { gap: 0; font-size: .8rem; padding: .3rem .4rem; }
            .controls .nav-label, .page-jump-label { display: none; }
            .controls .nav-ico { font-size: .95rem; }
            .page-indicator { min-width: 62px; font-size: .86rem; }
            .page-jump { gap: .22rem; }
            .page-jump-input { width: 2.7rem; height: 30px; }
            .page-jump-btn { height: 30px; padding: 0 .32rem; font-size: .68rem; }

            .lab-submenu { width: 96%; max-height: 70vh; border-radius: 12px; }
            .submenu-content { padding: 12px; }
        }

        /* ============ 响应式：超小屏 ============ */
        @media (max-width: 380px) {
            :root { --controls-safe-height: 82px; }
            .chalkboard { padding: 12px 10px 18px; font-size: 12px; }
            .visualization { flex-basis: 186px; min-height: 186px; padding: 8px; }
            .cover-title { font-size: 27px; }
            .cover-visual { height: 168px; }
            .controls { gap: .36rem; padding: .42rem .55rem calc(.42rem + env(safe-area-inset-bottom, 0px)); }
            .page-indicator { min-width: 56px; font-size: .82rem; }
            .page-jump-input { width: 2.45rem; height: 28px; }
            .page-jump-btn { height: 28px; font-size: .64rem; }
        }