/* ============================================================
   WPF Academy – design tokens
   ============================================================ */
:root {
  --bg: #f5f6fb;
  --surface: #ffffff;
  --surface-2: #eef0f8;
  --surface-3: #e4e7f3;
  --text: #171a26;
  --text-2: #444b5e;
  --muted: #6c7489;
  --line: #dfe3ef;
  --brand: #6c4cf5;
  --brand-2: #8d74ff;
  --brand-ink: #ffffff;
  --brand-soft: rgba(108, 76, 245, .10);
  --junior: #12a06a;
  --mid: #2b7be4;
  --senior: #d6407a;
  --ok: #12a06a;
  --bad: #d63f55;
  --warn: #c98a07;
  --code-bg: #f3f4fb;
  --code-bar: #e8eaf5;
  --code-text: #232838;
  --stage-bg: #e9ecf6;
  --shadow: 0 1px 2px rgba(20, 24, 50, .06), 0 8px 24px rgba(20, 24, 50, .06);
  --shadow-lg: 0 12px 40px rgba(20, 24, 50, .18);
  --tk-com: #8790a6;
  --tk-str: #0e8a5d;
  --tk-num: #c0410c;
  --tk-kw: #7a35e8;
  --tk-ty: #0b68c8;
  --tk-fn: #a4580a;
  --tk-attr: #b4570a;
  --tk-tag: #c01863;
  --tk-pre: #6b7280;
  --tk-ext: #0b7690;
  --tk-brace: #94a0b8;
  --tk-punc: #64748b;
  --radius: 12px;
  --header-h: 58px;
  --font: "Inter", system-ui, -apple-system, "Segoe UI", "Noto Sans TC", "PingFang TC", "Microsoft JhengHei", "Helvetica Neue", Arial, sans-serif;
  --mono: "Cascadia Code", "JetBrains Mono", "SFMono-Regular", Consolas, "Liberation Mono", ui-monospace, monospace;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0d0f17;
    --surface: #151927;
    --surface-2: #1b2033;
    --surface-3: #242a40;
    --text: #e9ecf8;
    --text-2: #b9c0d6;
    --muted: #8590ab;
    --line: #272d44;
    --brand: #9a85ff;
    --brand-2: #b7a8ff;
    --brand-ink: #130e33;
    --brand-soft: rgba(154, 133, 255, .14);
    --junior: #37d29b;
    --mid: #6aa6ff;
    --senior: #ff7aa8;
    --ok: #37d29b;
    --bad: #ff7189;
    --warn: #f0b84a;
    --code-bg: #10131f;
    --code-bar: #181c2c;
    --code-text: #dfe4f5;
    --stage-bg: #202638;
    --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .25);
    --shadow-lg: 0 12px 40px rgba(0, 0, 0, .55);
    --tk-com: #6d7898;
    --tk-str: #7ee0b0;
    --tk-num: #ffb27a;
    --tk-kw: #b99aff;
    --tk-ty: #7cc4ff;
    --tk-fn: #ffd479;
    --tk-attr: #ffb86b;
    --tk-tag: #ff8fc0;
    --tk-pre: #9aa3b5;
    --tk-ext: #5fe0e8;
    --tk-brace: #7f8aa3;
    --tk-punc: #8f9ab0;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0d0f17;
  --surface: #151927;
  --surface-2: #1b2033;
  --surface-3: #242a40;
  --text: #e9ecf8;
  --text-2: #b9c0d6;
  --muted: #8590ab;
  --line: #272d44;
  --brand: #9a85ff;
  --brand-2: #b7a8ff;
  --brand-ink: #130e33;
  --brand-soft: rgba(154, 133, 255, .14);
  --junior: #37d29b;
  --mid: #6aa6ff;
  --senior: #ff7aa8;
  --ok: #37d29b;
  --bad: #ff7189;
  --warn: #f0b84a;
  --code-bg: #10131f;
  --code-bar: #181c2c;
  --code-text: #dfe4f5;
  --stage-bg: #202638;
  --shadow: 0 1px 2px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .25);
  --shadow-lg: 0 12px 40px rgba(0, 0, 0, .55);
  --tk-com: #6d7898;
  --tk-str: #7ee0b0;
  --tk-num: #ffb27a;
  --tk-kw: #b99aff;
  --tk-ty: #7cc4ff;
  --tk-fn: #ffd479;
  --tk-attr: #ffb86b;
  --tk-tag: #ff8fc0;
  --tk-pre: #9aa3b5;
  --tk-ext: #5fe0e8;
  --tk-brace: #7f8aa3;
  --tk-punc: #8f9ab0;
  color-scheme: dark;
}

/* ============================================================
   base
   ============================================================ */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--text); font: 16px/1.7 var(--font); -webkit-font-smoothing: antialiased; }
a { color: var(--brand); text-decoration: none; }
a:hover { text-decoration: underline; }
h1, h2, h3, h4 { line-height: 1.25; margin: 0; letter-spacing: -.01em; }
p { margin: 0 0 1em; }
code { font-family: var(--mono); font-size: .88em; background: var(--surface-2); padding: .12em .4em; border-radius: 6px; border: 1px solid var(--line); color: var(--text); word-break: break-word; }
kbd { font: 11px/1 var(--mono); padding: 3px 6px; border-radius: 5px; border: 1px solid var(--line); background: var(--surface-2); color: var(--muted); }
button { font: inherit; color: inherit; cursor: pointer; }
.muted { color: var(--muted); }
.center { text-align: center; }
.ico { flex: none; vertical-align: -3px; }
:focus-visible { outline: 2px solid var(--brand); outline-offset: 2px; }
::selection { background: var(--brand-soft); }

.btn { display: inline-flex; align-items: center; gap: 8px; padding: 9px 16px; border-radius: 10px; border: 1px solid var(--line); background: var(--surface); color: var(--text); font-weight: 600; font-size: 14px; line-height: 1.2; text-decoration: none !important; transition: transform .08s, background .15s, border-color .15s, box-shadow .15s; }
.btn:hover { border-color: var(--brand); }
.btn:active { transform: translateY(1px); }
.btn.primary { background: var(--brand); color: var(--brand-ink); border-color: transparent; }
.btn.primary:hover { filter: brightness(1.08); }
.btn.ghost { background: transparent; }
.btn.done { background: color-mix(in srgb, var(--ok) 16%, transparent); color: var(--ok); border-color: color-mix(in srgb, var(--ok) 40%, transparent); }
.btn.sm { padding: 6px 11px; font-size: 13px; border-radius: 8px; }
.btn.lg { padding: 13px 24px; font-size: 16px; border-radius: 12px; }
.eyebrow { display: inline-block; font: 600 12px/1 var(--mono); letter-spacing: .08em; text-transform: uppercase; color: var(--brand); background: var(--brand-soft); padding: 7px 11px; border-radius: 999px; margin-bottom: 18px; }
.lead { font-size: 18px; color: var(--text-2); max-width: 62ch; }
.page { max-width: 1080px; margin: 0 auto; padding: 40px 24px 80px; }
.page.center { text-align: center; padding-top: 100px; }

/* ============================================================
   header / footer
   ============================================================ */
.top { position: sticky; top: 0; z-index: 60; background: color-mix(in srgb, var(--surface) 88%, transparent); backdrop-filter: saturate(1.4) blur(14px); -webkit-backdrop-filter: saturate(1.4) blur(14px); border-bottom: 1px solid var(--line); height: var(--header-h); }
.top-in { height: 100%; max-width: 1500px; margin: 0 auto; padding: 0 16px; display: flex; align-items: center; gap: 14px; }
.brand { display: flex; align-items: center; gap: 10px; color: var(--text); text-decoration: none !important; font-size: 17px; letter-spacing: -.01em; }
.brand b { color: var(--brand); }
.logo { display: inline-flex; }
.nav { display: flex; gap: 2px; margin-left: 10px; }
.nav a { color: var(--text-2); padding: 8px 12px; border-radius: 8px; font-weight: 600; font-size: 14px; text-decoration: none; }
.nav a:hover { background: var(--surface-2); color: var(--text); }
.nav a.on { color: var(--brand); background: var(--brand-soft); }
.top-r { margin-left: auto; display: flex; align-items: center; gap: 8px; }
.hbtn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; height: 36px; min-width: 36px; padding: 0 10px; border: 1px solid var(--line); background: var(--surface); border-radius: 9px; color: var(--text-2); font-weight: 700; font-size: 13px; }
.hbtn:hover { border-color: var(--brand); color: var(--brand); }
.search-btn { color: var(--muted); font-weight: 500; min-width: 200px; justify-content: flex-start; }
.search-btn kbd { margin-left: auto; }
.burger { display: none; }
.prog { display: inline-flex; align-items: center; gap: 7px; padding: 0 6px; color: var(--text-2); text-decoration: none !important; font: 600 12px var(--mono); }
.ring-bg { stroke: var(--surface-3); }
.ring-fg { stroke: var(--brand); transition: stroke-dashoffset .5s; }
.ring.junior .ring-fg { stroke: var(--junior); } .ring.mid .ring-fg { stroke: var(--mid); } .ring.senior .ring-fg { stroke: var(--senior); }
.foot { border-top: 1px solid var(--line); background: var(--surface); margin-top: 40px; }
.foot-in { max-width: 1080px; margin: 0 auto; padding: 28px 24px; display: grid; gap: 6px; font-size: 14px; }
.scrim { display: none; }
.toast { position: fixed; left: 50%; bottom: 28px; transform: translate(-50%, 20px); background: var(--text); color: var(--bg); padding: 11px 18px; border-radius: 10px; font-weight: 600; font-size: 14px; opacity: 0; pointer-events: none; transition: .25s; z-index: 200; box-shadow: var(--shadow-lg); }
.toast.show { opacity: 1; transform: translate(-50%, 0); }

/* ============================================================
   home
   ============================================================ */
.hero { background: radial-gradient(900px 400px at 85% -10%, var(--brand-soft), transparent 70%), radial-gradient(700px 360px at 0% 0%, color-mix(in srgb, var(--mid) 12%, transparent), transparent 70%); border-bottom: 1px solid var(--line); }
.hero-in { max-width: 1240px; margin: 0 auto; padding: 64px 24px 56px; display: grid; grid-template-columns: minmax(0, 1.05fr) minmax(0, 1fr); gap: 44px; align-items: center; }
.hero h1 { font-size: clamp(32px, 4.6vw, 54px); letter-spacing: -.03em; line-height: 1.12; margin-bottom: 18px; }
.grad { background: linear-gradient(100deg, var(--brand), var(--mid)); -webkit-background-clip: text; background-clip: text; color: transparent; }
.cta { display: flex; flex-wrap: wrap; gap: 12px; margin: 26px 0 30px; }
.cta.center { justify-content: center; }
.stats { list-style: none; display: flex; flex-wrap: wrap; gap: 26px; margin: 0; padding: 0; }
.stats li { display: flex; flex-direction: column; }
.stats b { font-size: 28px; letter-spacing: -.02em; line-height: 1.1; }
.stats span { color: var(--muted); font-size: 13px; }
.hero-demo .demo { box-shadow: var(--shadow-lg); }
.sec { padding: 64px 0; }
.sec.alt { background: var(--surface); border-block: 1px solid var(--line); }
.sec-in { max-width: 1080px; margin: 0 auto; padding: 0 24px; }
.sec h2 { font-size: 30px; letter-spacing: -.02em; }
.sec .sub { color: var(--text-2); margin: 10px 0 28px; max-width: 60ch; }
.sec-in.center .sub { margin-inline: auto; }
.level-cards { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.lcard { display: block; background: var(--surface); border: 1px solid var(--line); border-radius: 16px; padding: 22px; color: var(--text); text-decoration: none !important; box-shadow: var(--shadow); position: relative; overflow: hidden; transition: transform .15s, border-color .15s; }
.lcard::before { content: ""; position: absolute; inset: 0 0 auto 0; height: 4px; background: var(--c); }
.lcard.junior { --c: var(--junior); } .lcard.mid { --c: var(--mid); } .lcard.senior { --c: var(--senior); }
.lcard:hover { transform: translateY(-3px); border-color: var(--c); }
.lc-top { display: flex; justify-content: space-between; align-items: center; margin-bottom: 14px; }
.lc-n { width: 34px; height: 34px; border-radius: 10px; display: grid; place-items: center; font: 700 15px var(--mono); background: color-mix(in srgb, var(--c) 16%, transparent); color: var(--c); }
.lcard h3 { font-size: 20px; margin-bottom: 8px; }
.lcard p { color: var(--text-2); font-size: 14.5px; margin-bottom: 14px; }
.lc-meta { display: flex; gap: 14px; color: var(--muted); font: 600 12px var(--mono); }
.feats { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; margin-top: 24px; }
.feat { background: var(--bg); border: 1px solid var(--line); border-radius: 14px; padding: 20px; }
.fi { width: 42px; height: 42px; display: grid; place-items: center; border-radius: 12px; background: var(--brand-soft); color: var(--brand); margin-bottom: 12px; }
.feat h4 { font-size: 16px; margin-bottom: 6px; }
.feat p { font-size: 14px; color: var(--text-2); margin: 0; }

/* ============================================================
   roadmap
   ============================================================ */
.rm-hero { border-bottom: 1px solid var(--line); background: radial-gradient(700px 300px at 90% 0%, var(--brand-soft), transparent 70%); }
.rm-in { max-width: 1080px; margin: 0 auto; padding: 48px 24px 36px; }
.rm-in h1 { font-size: clamp(28px, 4vw, 42px); margin-bottom: 12px; }
.rm-total { display: flex; align-items: center; gap: 16px; margin: 26px 0 18px; }
.rm-total b { display: block; font-size: 22px; line-height: 1.2; }
.rm-jump { display: flex; gap: 10px; flex-wrap: wrap; }
.pill { display: inline-block; padding: 7px 14px; border-radius: 999px; font-weight: 700; font-size: 13px; border: 1px solid var(--line); background: var(--surface); color: var(--text) !important; text-decoration: none !important; }
.pill.junior { border-color: var(--junior); color: var(--junior) !important; } .pill.mid { border-color: var(--mid); color: var(--mid) !important; } .pill.senior { border-color: var(--senior); color: var(--senior) !important; }
.rm-body { max-width: 1080px; margin: 0 auto; padding: 24px; }
.rm-level { --c: var(--brand); margin: 36px 0 56px; scroll-margin-top: 80px; }
.rm-level.junior { --c: var(--junior); } .rm-level.mid { --c: var(--mid); } .rm-level.senior { --c: var(--senior); }
.rm-lhead { display: flex; align-items: center; gap: 16px; padding: 20px 22px; border-radius: 16px; background: linear-gradient(120deg, color-mix(in srgb, var(--c) 18%, var(--surface)), var(--surface)); border: 1px solid color-mix(in srgb, var(--c) 40%, var(--line)); }
.lvl-n { width: 46px; height: 46px; border-radius: 14px; background: var(--c); color: #fff; display: grid; place-items: center; font: 800 20px var(--mono); flex: none; }
.lh-t { flex: 1; min-width: 0; }
.lh-t h2 { font-size: 24px; }
.lh-t p { margin: 4px 0 0; color: var(--text-2); font-size: 14.5px; }
.lh-r { display: flex; align-items: center; gap: 10px; }
.lh-s { display: flex; flex-direction: column; font: 600 12px var(--mono); color: var(--muted); }
.lh-s b { color: var(--text); font-size: 15px; }
.rm-goals { margin: 18px 4px 6px; }
.rm-goals h4 { font-size: 13px; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin-bottom: 8px; }
.rm-goals ul { margin: 0; padding: 0; list-style: none; display: grid; grid-template-columns: 1fr 1fr; gap: 6px 22px; }
.rm-goals li { position: relative; padding-left: 22px; font-size: 14.5px; color: var(--text-2); }
.rm-goals li::before { content: ""; position: absolute; left: 3px; top: .55em; width: 8px; height: 8px; border-radius: 50%; background: var(--c); }
.rm-spine { position: relative; display: flex; flex-direction: column; gap: 20px; padding: 28px 0 8px; }
.rm-spine::before { content: ""; position: absolute; left: 50%; top: 0; bottom: 0; width: 3px; transform: translateX(-50%); background: repeating-linear-gradient(to bottom, color-mix(in srgb, var(--c) 55%, transparent) 0 8px, transparent 8px 14px); border-radius: 2px; }
.rm-node { position: relative; width: calc(50% - 34px); }
.rm-node.l { align-self: flex-start; } .rm-node.r { align-self: flex-end; }
.rm-dot { position: absolute; top: 22px; width: 16px; height: 16px; border-radius: 50%; background: var(--surface); border: 4px solid var(--c); z-index: 1; }
.rm-node.l .rm-dot { right: -43px; } .rm-node.r .rm-dot { left: -43px; }
.rm-node.done .rm-dot { background: var(--c); }
.rm-card { background: var(--surface); border: 1px solid var(--line); border-radius: 14px; padding: 16px 18px; box-shadow: var(--shadow); }
.rm-node.done .rm-card { border-color: color-mix(in srgb, var(--c) 50%, var(--line)); }
.rc-head { display: flex; align-items: baseline; justify-content: space-between; gap: 10px; }
.rc-head h3 { font-size: 17px; }
.rc-n { font: 700 12px var(--mono); color: var(--c); }
.rc-d { margin: 4px 0 10px; color: var(--muted); font-size: 13.5px; }
.rm-lessons { list-style: none; padding: 0; margin: 8px 0 0; display: grid; gap: 2px; }
.rm-lessons a { display: flex; align-items: center; gap: 10px; padding: 7px 8px; border-radius: 8px; color: var(--text); font-size: 14.5px; text-decoration: none !important; }
.rm-lessons a:hover { background: var(--surface-2); }
.rm-lessons a.soon { color: var(--muted); }
.rm-lessons .lt { flex: 1; min-width: 0; }
.rm-lessons .lm { font: 600 11.5px var(--mono); color: var(--muted); }
.chk { width: 18px; height: 18px; border-radius: 50%; border: 2px solid var(--line); display: inline-grid; place-items: center; flex: none; color: #fff; }
.chk.on { background: var(--ok); border-color: var(--ok); }
.rm-check { margin-top: 26px; padding: 20px 22px; border-radius: 16px; border: 1px dashed color-mix(in srgb, var(--c) 55%, var(--line)); background: color-mix(in srgb, var(--c) 6%, var(--surface)); }
.rm-check h4 { font-size: 17px; margin-bottom: 2px; }
.rm-check ul { list-style: none; padding: 0; margin: 12px 0 0; display: grid; gap: 8px; }
.rm-check label { display: flex; gap: 10px; align-items: flex-start; cursor: pointer; font-size: 14.5px; }
.rm-check input { margin-top: 5px; accent-color: var(--c); width: 16px; height: 16px; }

/* ============================================================
   lesson layout
   ============================================================ */
.layout { display: grid; grid-template-columns: 290px minmax(0, 1fr) 240px; max-width: 1560px; margin: 0 auto; align-items: start; }
.side { position: sticky; top: var(--header-h); height: calc(100vh - var(--header-h)); overflow-y: auto; border-right: 1px solid var(--line); background: var(--surface); }
.side-in { padding: 14px 10px 40px; }
.sg { margin-bottom: 6px; --c: var(--brand); }
.sg.junior { --c: var(--junior); } .sg.mid { --c: var(--mid); } .sg.senior { --c: var(--senior); }
.sg summary { display: flex; align-items: center; gap: 9px; padding: 9px 10px; border-radius: 9px; cursor: pointer; font-weight: 800; font-size: 14px; list-style: none; user-select: none; }
.sg summary::-webkit-details-marker { display: none; }
.sg summary:hover { background: var(--surface-2); }
.sg-dot { width: 10px; height: 10px; border-radius: 50%; background: var(--c); }
.sg-t { flex: 1; }
.sg-n { font: 600 11px var(--mono); color: var(--muted); }
.sc { padding: 10px 12px 3px; font: 700 11px var(--mono); text-transform: uppercase; letter-spacing: .06em; color: var(--muted); }
.sg ul { list-style: none; margin: 0; padding: 0; }
.sg li a { display: flex; align-items: center; gap: 9px; padding: 6px 10px; border-radius: 8px; color: var(--text-2); font-size: 14px; line-height: 1.35; text-decoration: none !important; }
.sg li a:hover { background: var(--surface-2); color: var(--text); }
.sg li a.on { background: color-mix(in srgb, var(--c) 14%, transparent); color: var(--c); font-weight: 700; }
.sg li a.soon { opacity: .6; }
.sg li a .chk { width: 16px; height: 16px; }
.lesson { padding: 34px 44px 90px; max-width: 900px; min-width: 0; }
.crumbs { display: flex; align-items: center; gap: 8px; font-size: 13px; color: var(--muted); margin-bottom: 12px; }
.cr-level { font-weight: 800; }
.cr-level.junior { color: var(--junior); } .cr-level.mid { color: var(--mid); } .cr-level.senior { color: var(--senior); }
.lesson h1 { font-size: clamp(28px, 3.6vw, 38px); letter-spacing: -.025em; }
.lesson-sum { font-size: 17.5px; color: var(--text-2); margin: 12px 0 14px; }
.lesson-meta { display: flex; flex-wrap: wrap; gap: 8px 18px; color: var(--muted); font-size: 13px; padding-bottom: 20px; border-bottom: 1px solid var(--line); margin-bottom: 8px; }
.lesson-meta span { display: inline-flex; align-items: center; gap: 6px; }
.lesson-body h2 { font-size: 24px; margin: 44px 0 14px; padding-top: 8px; scroll-margin-top: 78px; }
.lesson-body h3 { font-size: 18.5px; margin: 28px 0 10px; }
.lesson-body ul, .lesson-body ol { padding-left: 1.4em; margin: 0 0 1.1em; }
.lesson-body li { margin: .3em 0; }
.lesson-body li::marker { color: var(--brand); }
.table-wrap { overflow-x: auto; margin: 0 0 1.3em; border: 1px solid var(--line); border-radius: 12px; background: var(--surface); }
table { border-collapse: collapse; width: 100%; font-size: 14.5px; }
th, td { text-align: left; padding: 10px 14px; border-bottom: 1px solid var(--line); vertical-align: top; }
th { background: var(--surface-2); font-size: 13px; letter-spacing: .02em; white-space: nowrap; }
tr:last-child td { border-bottom: 0; }
.toc { position: sticky; top: calc(var(--header-h) + 24px); padding: 0 16px; font-size: 13.5px; max-height: calc(100vh - var(--header-h) - 48px); overflow: auto; }
.toc-t { font: 700 11px var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin-bottom: 10px; }
.toc ul { list-style: none; margin: 0; padding: 0; border-left: 2px solid var(--line); }
.toc a { display: block; padding: 5px 12px; color: var(--muted); margin-left: -2px; border-left: 2px solid transparent; text-decoration: none !important; line-height: 1.4; }
.toc a:hover { color: var(--text); }
.toc a.on { color: var(--brand); border-left-color: var(--brand); font-weight: 600; }

/* callouts */
.callout { border-radius: 12px; padding: 14px 16px 14px 16px; margin: 0 0 1.3em; border: 1px solid var(--line); border-left-width: 4px; background: var(--surface); }
.co-title { font: 800 11.5px var(--mono); text-transform: uppercase; letter-spacing: .08em; margin-bottom: 4px; }
.co-body { font-size: 15px; color: var(--text-2); }
.callout.tip { border-left-color: var(--ok); background: color-mix(in srgb, var(--ok) 7%, var(--surface)); } .callout.tip .co-title { color: var(--ok); }
.callout.warn { border-left-color: var(--warn); background: color-mix(in srgb, var(--warn) 9%, var(--surface)); } .callout.warn .co-title { color: var(--warn); }
.callout.info { border-left-color: var(--mid); background: color-mix(in srgb, var(--mid) 7%, var(--surface)); } .callout.info .co-title { color: var(--mid); }

/* code blocks */
.codeblock { margin: 0 0 1.3em; border: 1px solid var(--line); border-radius: 12px; overflow: hidden; background: var(--code-bg); }
.cb-head { display: flex; align-items: center; justify-content: space-between; padding: 6px 8px 6px 14px; background: var(--code-bar); border-bottom: 1px solid var(--line); font: 700 11.5px var(--mono); color: var(--muted); letter-spacing: .04em; }
.copy { display: inline-flex; align-items: center; gap: 6px; background: transparent; border: 1px solid transparent; border-radius: 7px; padding: 4px 8px; color: var(--muted); font: 600 12px var(--font); }
.copy:hover { background: var(--surface-3); color: var(--text); }
.copy.ok { color: var(--ok); }
pre.code { margin: 0; padding: 14px 16px; overflow-x: auto; font: 13.2px/1.62 var(--mono); color: var(--code-text); tab-size: 4; }
pre.code code { background: none; border: 0; padding: 0; font: inherit; color: inherit; word-break: normal; }
.tk-com { color: var(--tk-com); font-style: italic; } .tk-str { color: var(--tk-str); } .tk-num { color: var(--tk-num); } .tk-kw { color: var(--tk-kw); font-weight: 600; }
.tk-ty { color: var(--tk-ty); } .tk-fn { color: var(--tk-fn); } .tk-attr { color: var(--tk-attr); } .tk-tag { color: var(--tk-tag); } .tk-pre { color: var(--tk-pre); }
.tk-ext { color: var(--tk-ext); font-weight: 600; } .tk-brace { color: var(--tk-brace); } .tk-punc { color: var(--tk-punc); }

/* prev/next */
.lesson-foot { display: grid; grid-template-columns: 1fr auto 1fr; gap: 14px; align-items: center; margin-top: 56px; padding-top: 26px; border-top: 1px solid var(--line); }
.pn { display: flex; flex-direction: column; gap: 2px; padding: 12px 16px; border: 1px solid var(--line); border-radius: 12px; background: var(--surface); color: var(--text) !important; text-decoration: none !important; min-width: 0; }
.pn:hover { border-color: var(--brand); }
.pn.next { text-align: right; align-items: flex-end; }
.pn-l { font: 700 11.5px var(--mono); color: var(--muted); text-transform: uppercase; letter-spacing: .06em; display: inline-flex; gap: 4px; align-items: center; }
.pn-t { font-weight: 700; font-size: 14.5px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; max-width: 100%; }

/* quiz */
.quiz { margin-top: 52px; padding: 24px; border-radius: 16px; background: var(--surface); border: 1px solid var(--line); box-shadow: var(--shadow); scroll-margin-top: 78px; }
.quiz h2 { font-size: 22px; margin-bottom: 4px; }
.qcard { margin-top: 18px; padding: 16px; border-radius: 12px; background: var(--bg); border: 1px solid var(--line); }
.qcard.ok { border-color: color-mix(in srgb, var(--ok) 50%, var(--line)); }
.qcard.bad { border-color: color-mix(in srgb, var(--bad) 50%, var(--line)); }
.qq { display: flex; gap: 12px; font-weight: 600; margin-bottom: 12px; }
.qn { flex: none; width: 26px; height: 26px; border-radius: 8px; background: var(--brand-soft); color: var(--brand); display: grid; place-items: center; font: 800 13px var(--mono); }
.opts { display: grid; gap: 8px; }
.opt { display: flex; align-items: flex-start; gap: 12px; text-align: left; padding: 10px 14px; border-radius: 10px; border: 1px solid var(--line); background: var(--surface); line-height: 1.5; font-size: 15px; transition: border-color .12s, background .12s; }
.opt:not(:disabled):hover { border-color: var(--brand); background: var(--brand-soft); }
.ol { flex: none; width: 22px; height: 22px; border-radius: 6px; background: var(--surface-2); display: grid; place-items: center; font: 700 12px var(--mono); color: var(--muted); }
.opt.correct { border-color: var(--ok); background: color-mix(in srgb, var(--ok) 12%, var(--surface)); }
.opt.correct .ol { background: var(--ok); color: #fff; }
.opt.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 10%, var(--surface)); }
.opt.wrong .ol { background: var(--bad); color: #fff; }
.opt:disabled { cursor: default; color: inherit; }
.why { margin-top: 12px; padding: 10px 14px; border-radius: 10px; background: var(--surface); border: 1px solid var(--line); font-size: 14.5px; color: var(--text-2); }
.q-sum { display: flex; align-items: center; gap: 16px; margin-top: 18px; min-height: 34px; }
.q-score { display: flex; flex-direction: column; }
.q-score b { font-size: 20px; }
.q-score span { font-size: 13.5px; color: var(--muted); }
.q-score.pass b { color: var(--ok); }

/* ============================================================
   demo (try it yourself)
   ============================================================ */
.demo { margin: 0 0 1.6em; border: 1px solid var(--line); border-radius: 14px; background: var(--surface); overflow: hidden; box-shadow: var(--shadow); }
.demo-bar { display: flex; align-items: center; justify-content: space-between; gap: 10px; padding: 8px 10px 8px 14px; background: var(--code-bar); border-bottom: 1px solid var(--line); flex-wrap: wrap; }
.demo-title { font-size: 13.5px; color: var(--text-2); }
.demo-title b { color: var(--brand); }
.demo-actions { display: flex; gap: 6px; flex-wrap: wrap; }
.demo-grid { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); }
.demo.stack .demo-grid { grid-template-columns: 1fr; }
.demo-left, .demo-right { min-width: 0; display: flex; flex-direction: column; }
.demo-left { border-right: 1px solid var(--line); }
.demo.stack .demo-left { border-right: 0; border-bottom: 1px solid var(--line); }
.demo-tabs { display: flex; gap: 2px; padding: 6px 8px 0; background: var(--code-bar); border-bottom: 1px solid var(--line); overflow-x: auto; }
.demo-tabs.single { }
.dt { display: inline-flex; align-items: center; gap: 6px; padding: 6px 12px; border: 0; background: transparent; color: var(--muted); font: 700 12px var(--mono); border-radius: 8px 8px 0 0; border-bottom: 2px solid transparent; white-space: nowrap; }
.dt:hover { color: var(--text); }
.dt.on { color: var(--brand); border-bottom-color: var(--brand); background: var(--code-bg); }
.badge { background: var(--warn); color: #fff; border-radius: 999px; font: 700 10px var(--mono); padding: 1px 6px; }
.editor { background: var(--code-bg); max-height: 440px; overflow: auto; flex: 1; min-height: 120px; }
.editor-inner { position: relative; display: inline-block; min-width: 100%; vertical-align: top; }
.editor-hl, .editor-ta { margin: 0; padding: 14px 16px; font: 13px/1.6 var(--mono); tab-size: 4; white-space: pre; letter-spacing: 0; word-spacing: 0; border: 0; text-align: left; }
.editor-hl { color: var(--code-text); min-height: 100%; pointer-events: none; }
.editor-hl code { background: none; border: 0; padding: 0; font: inherit; color: inherit; word-break: normal; }
.editor-ta { position: absolute; inset: 0; width: 100%; height: 100%; background: transparent; color: transparent; caret-color: var(--text); resize: none; outline: none; overflow: hidden; }
.editor-ta::selection { background: color-mix(in srgb, var(--brand) 32%, transparent); color: transparent; }
.editor.readonly { opacity: .92; }
.demo-left .codeblock { margin: 0; border: 0; border-radius: 0; flex: 1; max-height: 440px; overflow: auto; }
.demo-preview { background: var(--stage-bg); flex: 1 0 auto; min-height: 150px; overflow: auto; position: relative; }
.demo-tree, .demo-output { flex: 1 0 auto; margin: 0; padding: 14px 16px; background: var(--code-bg); font: 12.5px/1.6 var(--mono); color: var(--code-text); overflow: auto; min-height: 150px; max-height: 440px; }
.out-line { padding: 4px 0; border-bottom: 1px dashed var(--line); white-space: pre-wrap; word-break: break-word; }
.out-line.warn::before { content: "⚠ "; color: var(--warn); } .out-line.err { color: var(--bad); } .out-line.log::before { content: "› "; color: var(--muted); }
.out-empty { color: var(--muted); font-family: var(--font); }
.demo-knobs { display: flex; flex-wrap: wrap; gap: 10px 22px; padding: 12px 16px; border-top: 1px solid var(--line); background: var(--surface); }
.demo-knobs.disabled { opacity: .45; pointer-events: none; }
.knob { display: inline-flex; align-items: center; gap: 8px; font-size: 13.5px; color: var(--text-2); }
.knob span { font-weight: 700; }
.knob select, .knob input[type=text] { font: 13px var(--mono); padding: 4px 8px; border-radius: 7px; border: 1px solid var(--line); background: var(--bg); color: var(--text); }
.knob input[type=range] { accent-color: var(--brand); width: 120px; }
.knob output { font: 600 12px var(--mono); color: var(--brand); min-width: 28px; }
.demo-note { padding: 10px 16px; border-top: 1px solid var(--line); font-size: 14px; color: var(--text-2); background: var(--surface); }
.widget { margin: 0 0 1.6em; border: 1px solid var(--line); border-radius: 14px; background: var(--surface); box-shadow: var(--shadow); overflow: hidden; }
.rawhtml { margin-bottom: 1.2em; }

/* ============================================================
   interview cards
   ============================================================ */
.tabs { display: flex; flex-wrap: wrap; gap: 8px; margin: 24px 0 14px; }
.tab { padding: 8px 16px; border-radius: 999px; border: 1px solid var(--line); background: var(--surface); color: var(--text-2) !important; font-weight: 700; font-size: 14px; text-decoration: none !important; }
.tab.on { background: var(--brand); border-color: var(--brand); color: var(--brand-ink) !important; }
.fc-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 16px; margin-top: 12px; }
.fc { perspective: 1200px; cursor: pointer; --c: var(--brand); }
.fc.junior { --c: var(--junior); } .fc.mid { --c: var(--mid); } .fc.senior { --c: var(--senior); }
.fc-in { position: relative; display: grid; width: 100%; height: 100%; transition: transform .5s; transform-style: preserve-3d; }
.fc.flipped .fc-in { transform: rotateY(180deg); }
.fc-face { grid-area: 1 / 1; min-height: 230px; backface-visibility: hidden; -webkit-backface-visibility: hidden; border-radius: 14px; padding: 18px; background: var(--surface); border: 1px solid var(--line); border-top: 4px solid var(--c); box-shadow: var(--shadow); display: flex; flex-direction: column; }
.fc-face.back { transform: rotateY(180deg); background: color-mix(in srgb, var(--c) 7%, var(--surface)); }
.fc-lv { font: 800 11px var(--mono); text-transform: uppercase; letter-spacing: .08em; color: var(--c); margin-bottom: 10px; }
.fc-q { font-weight: 700; font-size: 16.5px; line-height: 1.45; flex: 1; }
.fc-hint { margin-top: 12px; font: 600 11.5px var(--mono); color: var(--muted); }
.fc-a { font-size: 14.5px; color: var(--text-2); line-height: 1.6; }
.fc-a ul { padding-left: 1.2em; margin: .4em 0 0; }

/* ============================================================
   playground
   ============================================================ */
.page.pg { max-width: 1500px; }
.pg-head { display: flex; align-items: flex-end; justify-content: space-between; gap: 16px; flex-wrap: wrap; margin-bottom: 16px; }
.pg-head h1 { font-size: 28px; }
.pg-head p { margin: 4px 0 0; }
.pg-actions { display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.pg-sel { font: 13px var(--font); padding: 7px 10px; border-radius: 8px; border: 1px solid var(--line); background: var(--surface); color: var(--text); }
.pg-grid { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); border: 1px solid var(--line); border-radius: 14px; overflow: hidden; background: var(--surface); box-shadow: var(--shadow); min-height: 560px; }
.pg-left, .pg-right { display: flex; flex-direction: column; min-width: 0; }
.pg-left { border-right: 1px solid var(--line); }
.pg-left .editor { max-height: none; height: 600px; }
.pg-prev { min-height: 420px; }
.pg-details { border-top: 1px solid var(--line); background: var(--code-bg); }
.pg-details summary { padding: 8px 14px; cursor: pointer; font: 700 12px var(--mono); color: var(--muted); }
.pg-out { max-height: 180px; min-height: 60px; }

/* ============================================================
   search palette
   ============================================================ */
.palette { position: fixed; inset: 0; z-index: 300; background: rgba(8, 10, 20, .55); backdrop-filter: blur(3px); display: flex; justify-content: center; align-items: flex-start; padding-top: 12vh; }
.pal-box { width: min(640px, calc(100vw - 32px)); background: var(--surface); border: 1px solid var(--line); border-radius: 16px; box-shadow: var(--shadow-lg); overflow: hidden; }
.pal-in { display: flex; align-items: center; gap: 12px; padding: 14px 16px; border-bottom: 1px solid var(--line); color: var(--muted); }
.pal-in input { flex: 1; border: 0; outline: 0; background: transparent; font: 17px var(--font); color: var(--text); min-width: 0; }
.pal-list { list-style: none; margin: 0; padding: 6px; max-height: 50vh; overflow: auto; }
.pal-item { display: flex; gap: 12px; align-items: center; padding: 10px 12px; border-radius: 10px; cursor: pointer; }
.pal-item.on { background: var(--brand-soft); }
.pdot { width: 9px; height: 9px; border-radius: 50%; flex: none; background: var(--brand); }
.pdot.junior { background: var(--junior); } .pdot.mid { background: var(--mid); } .pdot.senior { background: var(--senior); }
.pt { font-weight: 700; font-size: 15px; }
.ps { color: var(--muted); font-size: 13px; display: -webkit-box; -webkit-line-clamp: 1; -webkit-box-orient: vertical; overflow: hidden; }
.pal-empty { padding: 24px; text-align: center; color: var(--muted); }
.pal-foot { display: flex; gap: 18px; padding: 8px 16px; border-top: 1px solid var(--line); color: var(--muted); font: 12px var(--mono); }

/* ============================================================
   responsive
   ============================================================ */
@media (max-width: 1260px) {
  .layout { grid-template-columns: 270px minmax(0, 1fr); }
  .toc { display: none; }
}
@media (max-width: 1100px) {
  .search-btn .sb-t, .search-btn kbd { display: none; }
  .search-btn { min-width: 36px; }
  .nav a { padding: 8px 9px; }
}
@media (max-width: 920px) {
  .burger { display: inline-flex; }
  .nav { display: none; }
  .layout { grid-template-columns: minmax(0, 1fr); }
  .side { position: fixed; z-index: 70; left: 0; top: var(--header-h); bottom: 0; width: min(86vw, 320px); height: auto; transform: translateX(-102%); transition: transform .25s; box-shadow: var(--shadow-lg); }
  body.nav-open .side { transform: none; }
  body.nav-open .scrim { display: block; position: fixed; inset: 0; z-index: 65; background: rgba(8, 10, 20, .45); }
  .lesson { padding: 24px 16px 70px; }
  .hero-in { grid-template-columns: 1fr; padding-top: 40px; }
  .level-cards, .feats { grid-template-columns: 1fr; }
  .rm-goals ul { grid-template-columns: 1fr; }
  .rm-spine::before { left: 12px; }
  .rm-node { width: auto; margin-left: 40px; }
  .rm-node.l, .rm-node.r { align-self: stretch; }
  .rm-node.l .rm-dot, .rm-node.r .rm-dot { left: -36px; right: auto; }
  .rm-lhead { flex-wrap: wrap; }
  .lh-t { flex: 1 1 calc(100% - 70px); }
  .lh-r { width: 100%; justify-content: flex-start; padding-left: 62px; }
  .pg-grid { grid-template-columns: 1fr; }
  .pg-left { border-right: 0; border-bottom: 1px solid var(--line); }
  .pg-left .editor { height: 340px; }
}
@media (max-width: 760px) {
  .demo-grid { grid-template-columns: 1fr; }
  .demo-left { border-right: 0; border-bottom: 1px solid var(--line); }
  .lesson-foot { grid-template-columns: 1fr; }
  .pn.next { text-align: left; align-items: flex-start; }
  .top-in { padding: 0 10px; gap: 8px; }
  .brand-t { display: none; }
  .prog-t { display: none; }
}
@media print {
  .top, .side, .toc, .lesson-foot, .foot, .demo-actions { display: none !important; }
  .layout { display: block; }
}