:root {
  color-scheme: light;
  --ink: #17313c;
  --muted: #4d6873;
  --quiet: #617d86;
  --line: rgba(42, 92, 108, .19);
  --surface: #ffffff;
  --base: #f6fafb;
  --serif: 'Noto Serif SC', 'Songti SC', 'STSong', serif;
  --sans: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, sans-serif;
  --mono: 'DM Mono', ui-monospace, SFMono-Regular, monospace;
  --accent: #197a91;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body { margin: 0; min-width: 320px; background: var(--base); color: var(--ink); font-family: var(--sans); }
body::before { content: ''; position: fixed; z-index: -1; inset: 0; pointer-events: none; background: radial-gradient(circle at 78% 4%, rgba(129, 206, 218, .21), transparent 38%), radial-gradient(circle at 10% 75%, rgba(223, 236, 226, .43), transparent 35%); }
a { color: inherit; text-decoration: none; }
button, a { -webkit-tap-highlight-color: transparent; }
a:focus-visible { outline: 2px solid var(--accent); outline-offset: 5px; border-radius: 3px; }
.container { width: min(1320px, calc(100% - 96px)); margin-inline: auto; }
.skip { position: absolute; z-index: 100; left: 18px; top: -80px; padding: 10px 16px; background: var(--ink); color: var(--base); }
.skip:focus { top: 16px; }

.site-header { min-height: 90px; border-bottom: 1px solid var(--line); background: rgba(255, 255, 255, .76); }
.header-inner { display: flex; align-items: center; justify-content: space-between; min-height: 90px; gap: 30px; }
.brand { display: flex; align-items: center; gap: 14px; min-width: 195px; font-family: var(--serif); font-size: 17px; font-weight: 600; letter-spacing: .07em; }
.brand-mark { display: block; flex: none; width: 42px; height: 42px; border-radius: 11px; }
.brand small { display: block; margin-top: 4px; color: var(--quiet); font-family: var(--mono); font-size: 9px; font-weight: 400; letter-spacing: .2em; }
.header-actions { display: flex; align-items: center; justify-content: flex-end; gap: 26px; }
.site-nav { display: flex; flex-wrap: wrap; align-items: center; justify-content: flex-end; gap: 8px 30px; }
.site-nav a { padding: 8px 0; color: var(--muted); font-size: 13px; letter-spacing: .06em; transition: color .2s; }
.site-nav a:hover, .site-nav a[aria-current] { color: var(--ink); }
.site-nav a[aria-current]::after { display: block; height: 1px; margin-top: 6px; background: var(--accent); content: ''; }
.language-switch { display: inline-flex; flex: none; align-items: center; gap: 6px; padding: 8px 11px; border: 1px solid var(--line); border-radius: 999px; background: #fff; color: var(--muted); font: 11px var(--sans); cursor: pointer; }
.language-switch:hover { border-color: var(--accent); }
.language-switch:focus-visible { outline: 2px solid var(--accent); outline-offset: 3px; }
.language-divider { color: var(--quiet); }
:root:not([data-lang="en"]) .language-option-zh, :root[data-lang="en"] .language-option-en { color: var(--ink); font-weight: 700; }
:root[data-lang="en"] .english { display: none; }
:root[data-lang="en"] .brand { font-size: 14px; letter-spacing: 0; }
:root[data-lang="en"] .home-hero h1 { font-size: clamp(52px, 5.4vw, 82px); }

.eyebrow { color: var(--accent); font: 11px/1.6 var(--mono); letter-spacing: .2em; text-transform: uppercase; }
.eyebrow-line { display: inline-flex; align-items: center; gap: 15px; }
.eyebrow-line::before { width: 28px; height: 1px; background: currentColor; content: ''; }
.serif { font-family: var(--serif); font-weight: 500; }
.muted { color: var(--muted); }
.arrow { font: 18px var(--mono); }
.text-link { display: inline-flex; align-items: center; gap: 12px; color: var(--accent); font-size: 13px; font-weight: 600; }
.text-link:hover .arrow { transform: translateX(5px); }
.text-link .arrow { transition: transform .2s; }
.breadcrumb { display: flex; flex-wrap: wrap; gap: 9px; padding: 29px 0 0; color: var(--quiet); font-size: 12px; }
.breadcrumb a:hover { color: var(--ink); }
.breadcrumb strong { color: var(--ink); font-weight: 500; }
.breadcrumb span { opacity: .45; }

.home-hero { display: grid; grid-template-columns: 1.05fr .95fr; min-height: 570px; align-items: center; gap: 30px; border-bottom: 1px solid var(--line); }
.home-hero h1 { margin: 27px 0 22px; font-size: clamp(52px, 6.3vw, 102px); line-height: 1.24; letter-spacing: -.045em; }
.home-hero h1 em { color: var(--accent); font-style: normal; }
.home-hero p { max-width: 610px; margin: 0; color: var(--muted); font-size: 16px; line-height: 2; }
.hero-note { display: flex; flex-wrap: wrap; align-items: center; gap: 22px; margin-top: 42px; }
.hero-note .tiny { color: var(--quiet); font: 10px var(--mono); letter-spacing: .11em; }
.scientific-window { position: relative; width: min(100%, 520px); aspect-ratio: 1; margin-inline: auto; overflow: hidden; border: 1px solid rgba(47, 125, 146, .2); border-radius: 50%; background: radial-gradient(circle at 50% 50%, #e1f3f4, #f8fcfb 31%, #e7f4f5 72%, #daeaf0); box-shadow: 0 28px 70px rgba(67, 134, 151, .13); }
.scientific-window::before, .scientific-window::after { position: absolute; inset: 14%; border: 1px solid rgba(36, 117, 139, .23); border-radius: 50%; content: ''; }
.scientific-window::after { inset: 28%; border-style: dashed; opacity: .65; }
.scientific-window .axis-x, .scientific-window .axis-y { position: absolute; background: rgba(47, 125, 146, .15); }
.scientific-window .axis-x { top: 50%; width: 100%; height: 1px; }
.scientific-window .axis-y { left: 50%; height: 100%; width: 1px; }
.scientific-window .core { position: absolute; top: 50%; left: 50%; width: 54px; height: 54px; border: 1px solid #9ad3d9; border-radius: 50%; background: radial-gradient(circle at 37% 34%, #ffffff, #83c7d1 30%, #2b7b91 75%); box-shadow: 0 0 58px rgba(49, 149, 173, .27); transform: translate(-50%, -50%); }
.orbit { position: absolute; inset: 9%; border: 1px solid rgba(45, 122, 143, .27); border-radius: 50%; transform: rotate(-25deg) scaleY(.62); }
.orbit.orbit-2 { inset: 21%; transform: rotate(29deg) scaleY(.62); }
.orbit.orbit-3 { inset: 35%; transform: rotate(-33deg) scaleY(.62); }
.plot-node { position: absolute; width: 11px; height: 11px; border-radius: 50%; background: var(--node); box-shadow: 0 0 22px var(--node); }
.node-a { --node: #197a91; left: 22%; top: 25%; }.node-b { --node: #ba572e; right: 18%; top: 38%; }.node-c { --node: #428258; right: 26%; bottom: 20%; }.node-d { --node: #8058a5; left: 17%; bottom: 31%; }
.plot-label { position: absolute; color: var(--label); font: 10px var(--mono); letter-spacing: .18em; text-transform: uppercase; }
.label-a { --label: #197a91; left: 12%; top: 18%; }.label-b { --label: #ba572e; right: 9%; top: 30%; }.label-c { --label: #428258; right: 20%; bottom: 16%; }.label-d { --label: #8058a5; left: 9%; bottom: 22%; }
.window-index { position: absolute; left: 50%; bottom: 7%; color: var(--quiet); font: 10px var(--mono); letter-spacing: .16em; transform: translateX(-50%); white-space: nowrap; }

.section-heading { display: flex; align-items: end; justify-content: space-between; gap: 20px; padding: 74px 0 28px; }
.section-heading h2 { margin: 9px 0 0; font: 500 clamp(28px, 3vw, 42px)/1.3 var(--serif); }
.section-heading p { max-width: 390px; margin: 0; color: var(--muted); font-size: 13px; line-height: 1.8; }
.subject-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 16px; padding-bottom: 98px; }
.subject-card { position: relative; display: grid; grid-template-columns: 1fr 150px; min-height: 270px; gap: 16px; overflow: hidden; padding: 30px 34px; border: 1px solid var(--line); background: linear-gradient(135deg, #ffffff 48%, color-mix(in srgb, var(--accent), white 91%)); box-shadow: 0 12px 35px rgba(34, 92, 109, .055); transition: border-color .2s, transform .2s, box-shadow .2s; }
.subject-card:hover { transform: translateY(-4px); border-color: color-mix(in srgb, var(--accent), transparent 40%); box-shadow: 0 18px 40px rgba(34, 92, 109, .12); }
.subject-card .subject-no { color: var(--accent); font: 11px var(--mono); letter-spacing: .16em; }
.subject-card h3 { margin: 22px 0 4px; font: 500 clamp(28px, 3vw, 39px) var(--serif); }
.subject-card .english { color: var(--accent); font: 11px var(--mono); letter-spacing: .14em; text-transform: uppercase; }
.subject-card p { max-width: 330px; margin: 21px 0 0; color: var(--muted); font-size: 13px; line-height: 1.8; }
.subject-card .card-bottom { position: absolute; bottom: 27px; left: 34px; color: var(--accent); font: 11px var(--mono); letter-spacing: .07em; }
.subject-card svg { width: 100%; max-height: 180px; align-self: center; justify-self: center; overflow: visible; opacity: .9; }

.subject-hero { display: grid; grid-template-columns: 1.12fr .88fr; min-height: 405px; gap: 50px; align-items: center; border-bottom: 1px solid var(--line); }
.subject-hero h1 { margin: 20px 0 5px; font: 500 clamp(58px, 6.5vw, 100px)/1.2 var(--serif); letter-spacing: -.04em; }
.subject-hero .english { color: var(--accent); font: 12px var(--mono); letter-spacing: .28em; text-transform: uppercase; }
.subject-hero p { max-width: 620px; margin: 28px 0 0; color: var(--muted); font-size: 16px; line-height: 1.9; }
.subject-hero .subject-art { display: grid; place-items: center; min-height: 300px; }
.subject-hero svg { width: min(100%, 350px); height: auto; }
.status-pill { display: inline-flex; align-items: center; gap: 8px; padding: 7px 12px; border: 1px solid color-mix(in srgb, var(--accent), transparent 55%); border-radius: 99px; color: var(--accent); font: 11px var(--mono); letter-spacing: .04em; }
.status-pill::before { width: 5px; height: 5px; border-radius: 50%; background: currentColor; content: ''; }
.topic-list, .lesson-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 16px; padding-bottom: 104px; }
.topic-card, .lesson-card { position: relative; min-height: 238px; padding: 30px 33px; border: 1px solid var(--line); background: #ffffff; box-shadow: 0 10px 30px rgba(34, 92, 109, .045); transition: border-color .2s, transform .2s; }
.topic-card:hover, a.lesson-card:hover { border-color: var(--accent); transform: translateY(-3px); }
.lesson-card-pending { background: #f1f6f7; }
.topic-card h3, .lesson-card h3 { margin: 27px 0 7px; font: 500 clamp(27px, 2.6vw, 37px) var(--serif); }
.topic-card .english, .lesson-card .english { color: var(--accent); font: 10px var(--mono); letter-spacing: .15em; text-transform: uppercase; }
.topic-card p, .lesson-card p { max-width: 440px; margin: 20px 0 22px; color: var(--muted); font-size: 14px; line-height: 1.8; }
.topic-card .card-go, .lesson-card .card-go { display: inline-flex; align-items: center; gap: 10px; color: var(--accent); font-size: 12px; }
.lesson-card .mode { color: var(--quiet); font: 11px var(--mono); letter-spacing: .05em; }
.empty-state { margin-bottom: 100px; padding: 58px; border: 1px solid var(--line); background: #ffffff; }
.empty-state h2 { margin: 20px 0 10px; font: 500 31px var(--serif); }
.empty-state p { max-width: 600px; color: var(--muted); line-height: 1.9; }
.topic-intro { display: flex; align-items: end; justify-content: space-between; gap: 40px; padding: 82px 0 58px; }
.topic-intro h1 { margin: 16px 0 8px; font: 500 clamp(54px, 6vw, 90px)/1.2 var(--serif); }
.topic-intro p { max-width: 580px; margin: 0; color: var(--muted); font-size: 16px; line-height: 1.9; }
.topic-visual { display: grid; place-items: center; flex: 0 0 220px; height: 220px; border: 1px solid var(--line); border-radius: 50%; background: radial-gradient(circle, #ccf2e6 0 6%, #d9b971 6% 9%, transparent 10% 24%, rgba(142,216,227,.28) 24.3% 24.8%, transparent 25% 42%, rgba(142,216,227,.2) 42.3% 42.8%, transparent 43%); }
.topic-visual span { color: var(--quiet); font: 9px var(--mono); letter-spacing: .1em; transform: translateY(85px); }
.topic-visual-physics { background: radial-gradient(circle at 50% 50%, #ba572e 0 7px, transparent 8px), linear-gradient(90deg, transparent 49.7%, rgba(186,87,46,.34) 50%, transparent 50.3%), linear-gradient(transparent 49.7%, rgba(186,87,46,.34) 50%, transparent 50.3%), radial-gradient(circle, transparent 0 32%, rgba(186,87,46,.28) 32.3% 33%, transparent 33.2% 55%, rgba(186,87,46,.16) 55.2% 56%, transparent 56.2%); }
.topic-visual-chemistry { background: radial-gradient(circle at 50% 50%, #8058a5 0 8px, transparent 9px), radial-gradient(ellipse 76px 31px at 50% 50%, transparent 96%, rgba(128,88,165,.45) 98% 100%, transparent 102%), radial-gradient(ellipse 31px 76px at 50% 50%, transparent 96%, rgba(25,122,145,.4) 98% 100%, transparent 102%), #f3f7f8; }
.topic-visual-biology { background: radial-gradient(circle at 52% 48%, #589971 0 18px, #b5dac2 19px 23px, transparent 24px), radial-gradient(circle at 27% 34%, #c9a874 0 7px, transparent 8px), radial-gradient(circle at 74% 65%, #b88bc4 0 9px, transparent 10px), radial-gradient(circle at 50% 50%, transparent 0 47%, rgba(66,130,88,.38) 47.5% 49%, transparent 49.5%), #f0f8f2; }
.context-bar { display: flex; justify-content: space-between; gap: 20px; padding: 22px 0; border-block: 1px solid var(--line); color: var(--muted); font-size: 12px; }
.site-footer { border-top: 1px solid var(--line); }
.footer-inner { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 20px; padding-block: 28px; color: var(--quiet); font: 11px var(--mono); letter-spacing: .06em; }

/* The entrance is a bright observation table; the lesson pages keep their own layouts. */
.home-page { background: #f8fbfc; }
.home-page::before { background: linear-gradient(90deg, rgba(38, 103, 117, .035) 1px, transparent 1px), linear-gradient(rgba(38, 103, 117, .035) 1px, transparent 1px); background-size: 44px 44px; mask-image: linear-gradient(to bottom, #000, transparent 760px); }
.home-page .site-header { background: rgba(255,255,255,.93); }
.home-hero { grid-template-columns: minmax(0, 1.04fr) minmax(0, .96fr); min-height: 700px; gap: clamp(34px, 5vw, 88px); }
.home-hero-copy { padding-block: 78px 86px; }
.home-hero h1 { margin: 28px 0 30px; font-size: clamp(59px, 6.1vw, 96px); line-height: 1.16; letter-spacing: -.055em; }
.home-hero h1 em { color: #147f93; }
.home-hero .hero-lead { max-width: 655px; color: #244754; font-size: 18px; line-height: 1.9; }
.home-hero .hero-detail { max-width: 650px; margin-top: 18px; color: var(--muted); font-size: 14px; line-height: 1.95; }
.hero-actions { display: flex; flex-wrap: wrap; align-items: center; gap: 25px; margin-top: 34px; }
.primary-link { display: inline-flex; align-items: center; justify-content: space-between; min-width: 176px; gap: 20px; padding: 16px 20px; border-radius: 8px; background: #123b4a; color: #fff; font-size: 14px; font-weight: 600; box-shadow: 0 10px 22px rgba(18, 59, 74, .17); transition: transform .2s, background .2s; }
.primary-link:hover { transform: translateY(-2px); background: #1a6172; }
.primary-link span { font-size: 18px; font-weight: 400; }
.discovery-board { position: relative; width: min(100%, 530px); margin-inline: auto; padding: 56px 17px 17px; overflow: hidden; border: 1px solid #d0e3e7; border-radius: 23px; background: #eaf3f4; box-shadow: 0 30px 75px rgba(21, 81, 95, .13); }
.discovery-board::before { position: absolute; inset: 0; background: linear-gradient(90deg, rgba(38,103,117,.06) 1px, transparent 1px), linear-gradient(rgba(38,103,117,.06) 1px, transparent 1px); background-size: 28px 28px; content: ''; pointer-events: none; }
.board-kicker { position: absolute; top: 23px; left: 25px; color: #416877; font: 10px var(--mono); letter-spacing: .17em; }
.board-grid { position: relative; display: grid; grid-template-columns: repeat(2, 1fr); gap: 11px; }
.board-panel { position: relative; display: grid; place-items: center; min-height: 202px; overflow: hidden; border: 1px solid color-mix(in srgb, var(--tile-accent), white 72%); border-radius: 12px; background: linear-gradient(150deg, white, color-mix(in srgb, var(--tile-accent), white 88%)); }
.board-panel::after { position: absolute; inset: 10px; border: 1px solid color-mix(in srgb, var(--tile-accent), transparent 83%); border-radius: 7px; content: ''; pointer-events: none; }
.board-panel-label { position: absolute; z-index: 1; bottom: 20px; left: 20px; color: var(--tile-accent); font: 11px var(--mono); letter-spacing: .1em; text-transform: uppercase; white-space: nowrap; }
.board-physics .board-panel-label, .board-chemistry .board-panel-label { right: 20px; left: auto; }
.board-panel svg { width: 72%; max-height: 152px; opacity: .95; transform: translateY(-10px); }
.board-physics svg { transform: translateY(-6px) rotate(6deg); }
.board-chemistry svg { transform: translateY(-10px) rotate(-7deg); }
.board-seal { position: absolute; z-index: 2; top: 53%; left: 50%; width: 72px; height: 72px; border: 5px solid #eaf3f4; border-radius: 18px; box-shadow: 0 12px 30px rgba(18,59,74,.2); transform: translate(-50%, -50%); }
.home-fields .section-heading { padding-top: 70px; }
.home-page .subject-card { min-height: 352px; padding-bottom: 75px; border-top: 4px solid var(--accent); border-radius: 6px; background: linear-gradient(125deg, #fff 48%, color-mix(in srgb, var(--accent), white 94%)); }
.home-page .subject-card h3 { margin-top: 18px; }
.home-page .subject-card p { max-width: 370px; margin-top: 21px; line-height: 1.9; }
.subject-topics { display: block; max-width: 360px; margin-top: 17px; color: var(--accent); font: 10px/1.7 var(--mono); letter-spacing: .02em; }
.home-page .subject-card svg { align-self: start; margin-top: 38px; }
.home-guide { display: grid; grid-template-columns: minmax(220px, .75fr) minmax(0, 1.6fr); gap: 38px 65px; padding: 70px 0 100px; border-top: 1px solid var(--line); }
.guide-heading h2 { max-width: 370px; margin: 16px 0; font: 500 clamp(30px, 3vw, 42px)/1.3 var(--serif); }
.guide-heading p { max-width: 340px; color: var(--muted); font-size: 14px; line-height: 1.8; }
.guide-steps { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; margin: 0; padding: 0; list-style: none; }
.guide-steps li { padding: 4px 0 0; border-top: 2px solid #bad4da; }
.guide-steps li > span { display: block; margin: 19px 0 22px; color: #1b8193; font: 13px var(--mono); }
.guide-steps h3 { margin: 0 0 12px; font-size: 17px; font-weight: 650; }
.guide-steps p { margin: 0; color: var(--muted); font-size: 13px; line-height: 1.85; }
.guide-note { grid-column: 2; display: grid; grid-template-columns: 130px 1fr; gap: 20px; padding: 22px 24px; border-left: 3px solid #69a9b4; background: #eef6f7; }
.guide-note strong { color: #1e6070; font-size: 12px; }
.guide-note p { margin: 0; color: var(--muted); font-size: 12px; line-height: 1.8; }


@media (max-width: 900px) {
  .container { width: min(100% - 48px, 1320px); }
  .home-hero { grid-template-columns: 1fr; padding-top: 58px; }
  .scientific-window { width: min(85%, 400px); margin-bottom: 50px; }
  .subject-hero { grid-template-columns: 1fr 260px; }
  .subject-card { grid-template-columns: 1fr 100px; }
  .home-hero { grid-template-columns: 1fr; min-height: auto; gap: 0; }
  .home-hero-copy { padding-bottom: 48px; }
  .discovery-board { margin-bottom: 60px; }
  .home-guide { grid-template-columns: 1fr; }
  .guide-note { grid-column: 1; }
}
@media (max-width: 680px) {
  .container { width: calc(100% - 36px); }
  .header-inner { flex-direction: column; align-items: flex-start; justify-content: center; gap: 8px; padding-block: 16px; }
  .header-actions { width: 100%; justify-content: space-between; gap: 10px; }
  .site-nav { justify-content: flex-start; gap: 5px 19px; }
  .site-nav a { font-size: 12px; }
  .home-hero { min-height: auto; }
  .home-hero h1 { font-size: clamp(47px, 11vw, 72px); }
  .home-hero p, .subject-hero p, .topic-intro p { font-size: 14px; }
  .scientific-window { width: min(100%, 350px); }
  .section-heading, .topic-intro { flex-direction: column; align-items: flex-start; gap: 16px; }
  .section-heading { padding-top: 54px; }
  .subject-grid, .topic-list, .lesson-grid { grid-template-columns: 1fr; gap: 12px; padding-bottom: 72px; }
  .subject-card { display: block; min-height: 290px; padding: 26px 26px 72px; }
  .subject-card h3 { max-width: 70%; }
  .subject-card p { max-width: 100%; }
  .subject-card .card-bottom { left: 26px; bottom: 24px; }
  .subject-card svg { position: absolute; top: 21px; right: 15px; width: 91px; opacity: .65; }
  .subject-hero { grid-template-columns: 1fr; gap: 0; padding-top: 34px; }
  .subject-hero .subject-art { min-height: 220px; }
  .subject-hero svg { width: 235px; }
  .topic-intro { padding: 60px 0 40px; }
  .topic-visual { flex: none; width: 150px; height: 150px; }
  .topic-visual span { transform: translateY(60px); }
  .context-bar { flex-direction: column; gap: 7px; }
  .empty-state { padding: 36px 26px; }
  .home-hero-copy { padding-block: 53px 42px; }
  .home-hero h1 { font-size: clamp(48px, 11vw, 69px); }
  :root[data-lang="en"] .home-hero h1 { font-size: clamp(45px, 10vw, 64px); }
  .home-hero .hero-lead { font-size: 15px; }
  .hero-actions { gap: 20px; }
  .discovery-board { width: 100%; padding: 44px 10px 10px; margin-bottom: 34px; }
  .board-kicker { top: 17px; left: 17px; font-size: 8px; }
  .board-grid { gap: 7px; }
  .board-panel { min-height: 145px; }
  .board-panel-label { bottom: 13px; left: 13px; font-size: 8px; }
  .board-physics .board-panel-label, .board-chemistry .board-panel-label { right: 13px; left: auto; }
  .board-panel svg { width: 78%; }
  .board-seal { width: 58px; height: 58px; }
  .home-page .subject-card { min-height: 370px; padding-bottom: 80px; }
  .home-page .subject-card h3 { max-width: 100%; }
  .home-page .subject-card svg { width: 78px; top: 32px; }
  .home-guide { padding: 50px 0 70px; gap: 30px; }
  .guide-steps { grid-template-columns: 1fr; gap: 28px; }
  .guide-steps li > span { margin: 14px 0; }
  .guide-note { grid-template-columns: 1fr; gap: 7px; }
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { transition-duration: .01ms !important; animation-duration: .01ms !important; }
}