:root {
        --bg: #f6f7fb;
        --bg-elevated: #ffffff;
        --text: #0f172a;
        --muted: #475569;
        --border: rgba(15, 23, 42, 0.08);
        --accent: #2563eb;
        --accent-soft: rgba(37, 99, 235, 0.12);
        --success: #059669;
        --danger: #dc2626;
        /* 产品图外框：浅蓝（与主色蓝系一致，避免偏绿） */
        --frame-accent: #5eb0ff;
        --frame-ring: color-mix(in srgb, var(--frame-accent) 48%, #dbeafe 52%);
        --frame-radius: 16px;
        --radius-lg: 20px;
        --radius-md: 14px;
        --shadow: 0 18px 50px rgba(15, 23, 42, 0.08);
        --shadow-sm: 0 8px 24px rgba(15, 23, 42, 0.06);
        --max: 1120px;
        --font: system-ui, -apple-system, "Segoe UI", Roboto, "PingFang SC",
          "Hiragino Sans GB", "Hiragino Sans", "Yu Gothic UI", "Microsoft YaHei",
          sans-serif;
      }

      @media (prefers-color-scheme: dark) {
        :root {
          --bg: #0b1220;
          --bg-elevated: #111827;
          --text: #e5e7eb;
          --muted: #94a3b8;
          --border: rgba(255, 255, 255, 0.08);
          --accent: #60a5fa;
          --accent-soft: rgba(96, 165, 250, 0.15);
          --shadow: 0 18px 50px rgba(0, 0, 0, 0.45);
          --shadow-sm: 0 8px 24px rgba(0, 0, 0, 0.35);
          --frame-accent: #7cc4ff;
          --frame-ring: color-mix(in srgb, var(--frame-accent) 52%, #1e3a8a 48%);
        }
      }

      *,
      *::before,
      *::after {
        box-sizing: border-box;
      }

      html {
        scroll-behavior: smooth;
      }

      body {
        margin: 0;
        font-family: var(--font);
        color: var(--text);
        background: radial-gradient(
            1200px 600px at 10% -10%,
            var(--accent-soft),
            transparent 55%
          ),
          var(--bg);
        line-height: 1.6;
      }

      a {
        color: var(--accent);
        text-decoration: none;
      }

      a:hover {
        text-decoration: underline;
      }

      a:focus-visible,
      button:focus-visible {
        outline: 2px solid var(--accent);
        outline-offset: 2px;
      }

      .wrap {
        width: min(var(--max), calc(100% - 40px));
        margin-inline: auto;
      }

      /* Nav */
      .nav {
        position: sticky;
        top: 0;
        z-index: 40;
        backdrop-filter: blur(12px);
        background: color-mix(in srgb, var(--bg) 82%, transparent);
        border-bottom: 1px solid var(--border);
      }

      .nav-inner {
        display: flex;
        align-items: center;
        justify-content: space-between;
        gap: 16px;
        padding: 14px 0;
      }

      .brand {
        display: flex;
        align-items: center;
        gap: 10px;
        font-weight: 700;
        letter-spacing: -0.02em;
        color: var(--text);
        text-decoration: none;
      }

      .brand:hover {
        text-decoration: none;
        opacity: 0.9;
      }

      .brand img {
        height: 36px;
        width: auto;
        display: block;
      }

      .nav-links {
        display: flex;
        flex-wrap: wrap;
        gap: 8px 18px;
        list-style: none;
        margin: 0;
        padding: 0;
        font-size: 0.95rem;
      }

      .nav-links a {
        color: var(--muted);
        text-decoration: none;
        padding: 6px 8px;
        border-radius: 10px;
      }

      .nav-links a:hover {
        color: var(--text);
        background: color-mix(in srgb, var(--text) 6%, transparent);
        text-decoration: none;
      }

      /* Hero */
      .hero {
        padding: 48px 0 32px;
      }

      .hero-grid {
        display: grid;
        grid-template-columns: 1.05fr 0.95fr;
        gap: 40px;
        align-items: center;
      }

      @media (min-width: 901px) {
        .hero-grid {
          align-items: center;
        }
      }

      @media (max-width: 900px) {
        .hero-grid {
          grid-template-columns: 1fr;
        }
      }

      .eyebrow {
        display: inline-flex;
        align-items: center;
        gap: 8px;
        font-size: 0.85rem;
        color: var(--muted);
        margin-bottom: 12px;
      }

      .eyebrow span {
        display: inline-block;
        width: 6px;
        height: 6px;
        border-radius: 999px;
        background: var(--accent);
      }

      /* 产品名：醒目一级，仍略小于下方 slogan（h1） */
      .hero .eyebrow {
        font-size: clamp(1.2rem, 2.85vw, 1.65rem);
        font-weight: 700;
        color: var(--text);
        margin-bottom: 10px;
        letter-spacing: -0.02em;
      }

      .hero .eyebrow span {
        width: 7px;
        height: 7px;
      }

      h1 {
        margin: 0 0 14px;
        font-size: clamp(1.85rem, 4vw, 2.6rem);
        line-height: 1.15;
        letter-spacing: -0.03em;
      }

      .lede {
        margin: 0 0 22px;
        color: var(--muted);
        font-size: 1.05rem;
        max-width: 46ch;
      }

      .cta-row {
        display: flex;
        flex-wrap: wrap;
        gap: 12px;
        margin-bottom: 18px;
      }

      .apk-note {
        margin: 0;
        max-width: 52ch;
        font-size: 0.88rem;
        line-height: 1.55;
        color: var(--muted);
      }

      .cta-row + .apk-note {
        margin-top: -8px;
        margin-bottom: 4px;
      }

      .btn {
        display: inline-flex;
        align-items: center;
        gap: 10px;
        border: 1px solid var(--border);
        background: var(--bg-elevated);
        color: var(--text);
        padding: 12px 16px;
        border-radius: 14px;
        font-weight: 600;
        font-size: 0.95rem;
        cursor: pointer;
        text-decoration: none;
        box-shadow: var(--shadow-sm);
        transition: transform 0.12s ease, box-shadow 0.12s ease,
          border-color 0.12s ease;
      }

      .btn:hover {
        transform: translateY(-1px);
        box-shadow: var(--shadow);
        text-decoration: none;
      }

      .btn-primary {
        border-color: color-mix(in srgb, var(--success) 35%, var(--border));
        background: linear-gradient(
          180deg,
          color-mix(in srgb, var(--success) 12%, var(--bg-elevated)),
          var(--bg-elevated)
        );
      }

      .btn-store {
        border-color: color-mix(in srgb, var(--danger) 35%, var(--border));
      }

      .btn-apple {
        border-color: color-mix(in srgb, var(--accent) 35%, var(--border));
      }

      .btn small {
        display: block;
        font-weight: 500;
        color: var(--muted);
        font-size: 0.78rem;
        margin-top: 2px;
      }

      .btn .stack {
        display: flex;
        flex-direction: column;
        align-items: flex-start;
        line-height: 1.2;
      }

      .hero-art {
        position: relative;
        display: flex;
        justify-content: center;
        align-self: center;
      }

      /* 产品图：略加厚描边 + 柔和外扩阴影，显得更饱满、轻松 */
      .app-shot-frame {
        display: block;
        overflow: hidden;
        border-radius: var(--frame-radius);
        border: 3px solid var(--frame-ring);
        box-shadow:
          0 0 0 1px color-mix(in srgb, var(--frame-ring) 35%, transparent),
          0 12px 40px color-mix(in srgb, var(--frame-accent) 16%, transparent);
        line-height: 0;
        background: color-mix(in srgb, var(--frame-accent) 8%, var(--bg-elevated));
      }

      .app-shot-frame img {
        display: block;
        width: 100%;
        height: auto;
        vertical-align: middle;
      }

      .hero-asset {
        width: 100%;
        /* 偏小插图 + 留白（类似 Duolingo 营销页节奏） */
        max-width: min(100%, clamp(240px, 26vw, 300px));
        margin: 0 auto;
      }

      @media (min-width: 901px) {
        .hero-art {
          justify-content: flex-end;
          padding-inline-end: clamp(0px, 4vw, 40px);
        }
      }

      .hero-asset .app-shot-frame {
        transition: transform 0.15s ease, box-shadow 0.15s ease;
      }

      .hero-asset .app-shot-frame:hover {
        transform: translateY(-2px);
        box-shadow:
          0 0 0 1px color-mix(in srgb, var(--frame-ring) 40%, transparent),
          0 18px 48px color-mix(in srgb, var(--frame-accent) 22%, transparent);
      }

      .hero-asset-caption {
        margin: 10px 0 0;
        font-size: 0.78rem;
        color: var(--muted);
        text-align: center;
        line-height: 1.4;
      }

      /* Sections */
      section {
        padding: 44px 0;
      }

      .section-title {
        margin: 0 0 10px;
        font-size: 1.35rem;
        letter-spacing: -0.02em;
      }

      .section-sub {
        margin: 0 0 28px;
        color: var(--muted);
        max-width: 62ch;
      }

      .split {
        display: grid;
        grid-template-columns: 1fr 1fr;
        gap: 32px;
        align-items: center;
      }

      @media (min-width: 901px) {
        .split.reverse .split-text {
          order: 2;
        }

        .split.reverse .split-visual {
          order: 1;
        }
      }

      @media (max-width: 900px) {
        .split {
          grid-template-columns: 1fr;
        }

        .split.reverse .split-text,
        .split.reverse .split-visual {
          order: unset;
        }
      }

      .list-lines p {
        margin: 0 0 12px;
        padding-left: 14px;
        border-left: 3px solid color-mix(in srgb, var(--accent) 55%, var(--border));
        color: var(--muted);
      }

      #growth .split-visual {
        width: 100%;
        max-width: min(100%, clamp(200px, 28vw, 280px));
        margin-inline: auto;
        justify-self: center;
      }

      @media (max-width: 900px) {
        #growth .split-visual {
          max-width: min(85vw, 260px);
        }
      }

      .split .app-shot-frame {
        max-width: 100%;
      }

      .split .app-shot-frame img {
        width: 100%;
        height: auto;
      }

      /* 学习形式：四宫格缩略图（整体收窄，留白更多） */
      .learning-grid {
        display: grid;
        grid-template-columns: repeat(2, 1fr);
        gap: 20px 16px;
        max-width: min(100%, 720px);
        margin-inline: auto;
      }

      @media (min-width: 900px) {
        .learning-grid {
          grid-template-columns: repeat(4, 1fr);
          max-width: min(100%, 800px);
        }
      }

      .learning-cell .shot {
        width: 100%;
      }

      .learning-caption {
        margin: 10px 0 0;
        font-size: 0.86rem;
        color: var(--muted);
        text-align: center;
        line-height: 1.35;
      }

      .shot.shot--block {
        display: block;
        width: 100%;
      }

      .hero-shot {
        width: 100%;
        appearance: none;
        -webkit-appearance: none;
        font: inherit;
        color: inherit;
        text-align: center;
      }

      .shot {
        border: none;
        padding: 0;
        margin: 0;
        background: none;
        cursor: zoom-in;
        border-radius: 0;
        box-shadow: none;
        transition: transform 0.12s ease;
      }

      .shot:hover {
        transform: translateY(-3px);
      }

      .shot:hover .app-shot-frame {
        box-shadow:
          0 0 0 1px color-mix(in srgb, var(--frame-ring) 42%, transparent),
          0 18px 48px color-mix(in srgb, var(--frame-accent) 24%, transparent);
      }

      .shot .app-shot-frame {
        height: 100%;
      }

      .shot img {
        display: block;
        width: 100%;
        height: auto;
      }

      .download-band {
        background: color-mix(in srgb, var(--accent-soft) 55%, var(--bg-elevated));
        border: 1px solid var(--border);
        border-radius: var(--radius-lg);
        padding: 26px 22px;
        box-shadow: var(--shadow-sm);
      }

      .download-band .cta-row {
        margin-bottom: 0;
      }

      /* Footer */
      footer {
        border-top: 1px solid var(--border);
        padding: 28px 0 40px;
        margin-top: 20px;
        color: var(--muted);
        font-size: 0.9rem;
      }

      .footer-grid {
        display: grid;
        grid-template-columns: 1fr 1fr 1fr;
        gap: 12px;
        align-items: start;
      }

      @media (max-width: 720px) {
        .footer-grid {
          grid-template-columns: 1fr;
          text-align: left;
        }
      }

      footer a {
        color: var(--muted);
        text-decoration: underline;
        text-underline-offset: 3px;
      }

      footer a:hover {
        color: var(--text);
      }

      footer p {
        margin: 0;
      }

      .text-end {
        text-align: right;
      }

      @media (max-width: 720px) {
        .footer-grid .text-end {
          text-align: left;
        }
      }

      /* Dialog */
      dialog {
        border: none;
        border-radius: 16px;
        padding: 0;
        max-width: min(92vw, 960px);
        background: var(--bg-elevated);
        color: var(--text);
        box-shadow: var(--shadow);
      }

      dialog::backdrop {
        background: rgba(15, 23, 42, 0.55);
      }

      .dialog-head {
        display: flex;
        justify-content: flex-end;
        padding: 10px 10px 0;
      }

      .dialog-body {
        padding: 0 14px 14px;
      }

      .dialog-body img {
        display: block;
        width: 100%;
        height: auto;
        border-radius: 12px;
      }

      .close-btn {
        border: 1px solid var(--border);
        background: var(--bg);
        color: var(--text);
        border-radius: 10px;
        padding: 8px 12px;
        cursor: pointer;
        font-weight: 600;
      }