/* ---------- Tokens ---------- */
:root {
  --bg: #f6f7f9;
  --surface: #ffffff;
  --surface-2: #f0f2f5;
  --border: #dde1e7;
  --text: #16191f;
  --muted: #5f6b7a;
  --accent: #ff9900;
  --accent-ink: #1a1300;
  --accent-soft: #fff3e0;
  --link: #0a6bcf;
  --navy: #232f3e;
  --ok: #1d8102;
  --ok-soft: #e9f6e5;
  --bad: #c42b1c;
  --bad-soft: #fdecea;
  --warn-soft: #fff6db;
  --info-soft: #e8f2fd;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 2px 8px rgba(16, 24, 40, .05);
  --radius: 12px;
  --sidebar-w: 270px;
  --topbar-h: 56px;
  --font: 'Inter', system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  --mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, monospace;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0f141b; --surface: #161d26; --surface-2: #1d2631; --border: #2b3542;
    --text: #e6eaf0; --muted: #9aa7b6; --accent-soft: #3a2a0d; --link: #6cb4ff;
    --ok: #5bd16a; --ok-soft: #13301a; --bad: #ff7a6b; --bad-soft: #3a1714;
    --warn-soft: #3a300f; --info-soft: #102a45;
    --shadow: 0 1px 2px rgba(0,0,0,.4), 0 2px 10px rgba(0,0,0,.25);
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0f141b; --surface: #161d26; --surface-2: #1d2631; --border: #2b3542;
  --text: #e6eaf0; --muted: #9aa7b6; --accent-soft: #3a2a0d; --link: #6cb4ff;
  --ok: #5bd16a; --ok-soft: #13301a; --bad: #ff7a6b; --bad-soft: #3a1714;
  --warn-soft: #3a300f; --info-soft: #102a45;
  --shadow: 0 1px 2px rgba(0,0,0,.4), 0 2px 10px rgba(0,0,0,.25);
  color-scheme: dark;
}

/* ---------- Base ---------- */
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--text);
  font-family: var(--font); font-size: 16px; line-height: 1.6;
}
a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; }
code { font-family: var(--mono); font-size: .88em; background: var(--surface-2); padding: .1em .35em; border-radius: 5px; }
h1, h2, h3, h4 { line-height: 1.25; margin: 0 0 .5em; }
h1 { font-size: clamp(1.6rem, 3vw, 2.2rem); letter-spacing: -.02em; }
h2 { font-size: 1.35rem; letter-spacing: -.01em; }
h3 { font-size: 1.1rem; }
p { margin: 0 0 1em; }
button, input, select { font: inherit; color: inherit; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }

/* ---------- Top bar & layout ---------- */
.topbar {
  position: sticky; top: 0; z-index: 30; height: var(--topbar-h);
  display: flex; align-items: center; gap: 12px; padding: 0 16px;
  background: var(--navy); color: #fff;
}
.brand { color: #fff; font-weight: 800; letter-spacing: -.01em; display: flex; align-items: center; gap: 10px; }
.brand:hover { text-decoration: none; }
.brand-mark { color: var(--accent); }
.topbar-right { margin-left: auto; display: flex; gap: 8px; }
.icon-btn {
  background: transparent; border: 1px solid rgba(255,255,255,.2); color: #fff;
  width: 38px; height: 38px; border-radius: 10px; cursor: pointer; font-size: 18px;
}
.icon-btn:hover { background: rgba(255,255,255,.08); }
.menu-btn { display: none; }

.layout { display: flex; min-height: calc(100vh - var(--topbar-h)); }
.sidebar {
  width: var(--sidebar-w); flex-shrink: 0; background: var(--surface);
  border-right: 1px solid var(--border); padding: 16px 12px 40px;
  position: sticky; top: var(--topbar-h); height: calc(100vh - var(--topbar-h)); overflow-y: auto;
}
.sidebar h4 { font-size: .72rem; text-transform: uppercase; letter-spacing: .08em; color: var(--muted); margin: 18px 10px 6px; }
.sidebar a {
  display: flex; align-items: center; gap: 10px; padding: 7px 10px; border-radius: 8px;
  color: var(--text); font-size: .93rem;
}
.sidebar a:hover { background: var(--surface-2); text-decoration: none; }
.sidebar a.active { background: var(--accent-soft); font-weight: 600; }
.sidebar .ico { width: 20px; text-align: center; }
.scrim { display: none; }
main { flex: 1; min-width: 0; padding: 32px clamp(16px, 4vw, 48px) 80px; outline: none; }
.wrap { max-width: 980px; margin: 0 auto; }
.wrap.narrow { max-width: 780px; }

@media (max-width: 900px) {
  .menu-btn { display: inline-block; }
  .sidebar {
    position: fixed; left: 0; top: var(--topbar-h); z-index: 25; transform: translateX(-100%);
    transition: transform .2s ease; box-shadow: var(--shadow);
  }
  body.nav-open .sidebar { transform: none; }
  body.nav-open .scrim { display: block; position: fixed; inset: var(--topbar-h) 0 0 0; background: rgba(0,0,0,.35); z-index: 20; }
  main { padding-top: 24px; }
}

/* ---------- Components ---------- */
.card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px; box-shadow: var(--shadow);
}
.grid { display: grid; gap: 16px; }
.grid.two { grid-template-columns: repeat(auto-fit, minmax(280px, 1fr)); }
.grid.three { grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); }
.stack > * + * { margin-top: 16px; }
.row { display: flex; gap: 12px; align-items: center; flex-wrap: wrap; }
.spacer { flex: 1; }
.muted { color: var(--muted); }
.small { font-size: .88rem; }
.center { text-align: center; }

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 9px 16px; border-radius: 10px; border: 1px solid var(--border);
  background: var(--surface); cursor: pointer; font-weight: 600; font-size: .94rem; color: var(--text);
}
.btn:hover { background: var(--surface-2); text-decoration: none; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--accent-ink); }
.btn.primary:hover { filter: brightness(1.05); }
.btn.ghost { background: transparent; }
.btn:disabled { opacity: .5; cursor: not-allowed; }
.btn.sm { padding: 6px 11px; font-size: .85rem; }

.pill {
  display: inline-block; padding: 2px 10px; border-radius: 999px; font-size: .78rem; font-weight: 600;
  background: var(--surface-2); color: var(--muted); border: 1px solid var(--border);
}
.pill.accent { background: var(--accent-soft); color: var(--text); border-color: transparent; }
.pill.ok { background: var(--ok-soft); color: var(--ok); border-color: transparent; }
.pill.bad { background: var(--bad-soft); color: var(--bad); border-color: transparent; }

.hero {
  background: linear-gradient(135deg, var(--navy), #37475a); color: #fff; border-radius: 18px;
  padding: clamp(24px, 5vw, 48px); margin-bottom: 28px; position: relative; overflow: hidden;
}
.hero h1 { color: #fff; }
.hero p { color: #d5dbe3; max-width: 640px; font-size: 1.05rem; }
.hero .btn { border-color: rgba(255,255,255,.25); background: rgba(255,255,255,.08); color: #fff; }
.hero .btn.primary { background: var(--accent); color: var(--accent-ink); border-color: var(--accent); }
.hero::after {
  content: ''; position: absolute; right: -60px; top: -60px; width: 260px; height: 260px;
  border: 40px solid rgba(255,153,0,.15); border-radius: 50%;
}

.track-card { display: flex; flex-direction: column; gap: 10px; }
.track-card .code { font-family: var(--mono); font-weight: 600; color: var(--accent); }
.track-card h3 { font-size: 1.25rem; margin: 0; }
.stats { display: flex; gap: 18px; flex-wrap: wrap; font-size: .88rem; color: var(--muted); }
.stats b { color: var(--text); }

.progress { height: 8px; background: var(--surface-2); border-radius: 99px; overflow: hidden; }
.progress > span { display: block; height: 100%; background: var(--accent); border-radius: 99px; transition: width .3s; }
.progress.ok > span { background: var(--ok); }

.domain-head { display: flex; align-items: baseline; gap: 12px; flex-wrap: wrap; margin-bottom: 6px; }
.weight { font-family: var(--mono); font-size: .85rem; color: var(--muted); }
.lesson-list { list-style: none; margin: 12px 0 0; padding: 0; }
.lesson-list li { border-top: 1px solid var(--border); }
.lesson-list a { display: flex; gap: 12px; align-items: center; padding: 11px 4px; color: var(--text); }
.lesson-list a:hover { background: var(--surface-2); text-decoration: none; }
.check { width: 22px; height: 22px; border-radius: 50%; border: 2px solid var(--border); flex-shrink: 0; display: grid; place-items: center; font-size: 12px; }
.check.done { background: var(--ok); border-color: var(--ok); color: #fff; }

.tabs { display: flex; gap: 6px; border-bottom: 1px solid var(--border); margin-bottom: 20px; overflow-x: auto; }
.tabs a { padding: 9px 14px; color: var(--muted); font-weight: 600; border-bottom: 2px solid transparent; white-space: nowrap; }
.tabs a.active { color: var(--text); border-color: var(--accent); }
.tabs a:hover { text-decoration: none; color: var(--text); }

.breadcrumb { font-size: .86rem; color: var(--muted); margin-bottom: 14px; }

/* ---------- Lesson prose ---------- */
.prose h2 { margin-top: 1.6em; padding-top: .2em; }
.prose ul, .prose ol { padding-left: 1.3em; margin: 0 0 1em; }
.prose li { margin: .25em 0; }
.prose table, .tool table {
  width: 100%; border-collapse: collapse; margin: 1em 0 1.4em; font-size: .9rem;
  display: block; overflow-x: auto;
}
.prose th, .prose td, .tool th, .tool td { border: 1px solid var(--border); padding: 8px 10px; text-align: left; vertical-align: top; }
.prose th, .tool th { background: var(--surface-2); font-weight: 600; }
.callout { background: var(--info-soft); border-left: 4px solid var(--link); padding: 12px 16px; border-radius: 8px; margin: 1em 0; }
.callout.warn { background: var(--warn-soft); border-left-color: var(--accent); }
.callout > :last-child { margin-bottom: 0; }
.keybox { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 18px 20px; margin-top: 24px; }
.keybox h3 { display: flex; gap: 8px; align-items: center; }
.keybox ul { margin: 0; padding-left: 1.2em; }
.keybox.tips { border-color: var(--accent); background: var(--accent-soft); }
.svc-tags { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 18px; }
.lesson-nav { display: flex; justify-content: space-between; gap: 12px; margin-top: 32px; flex-wrap: wrap; }

/* ---------- Quiz ---------- */
.q-meta { display: flex; gap: 8px; flex-wrap: wrap; margin-bottom: 10px; align-items: center; }
.q-stem { font-size: 1.05rem; font-weight: 500; margin-bottom: 16px; white-space: pre-line; }
.options { display: grid; gap: 10px; }
.opt {
  display: flex; gap: 12px; align-items: flex-start; text-align: left; width: 100%;
  padding: 12px 14px; border: 1.5px solid var(--border); border-radius: 10px; background: var(--surface);
  cursor: pointer; line-height: 1.45;
}
.opt:hover:not(:disabled) { border-color: var(--accent); }
.opt .letter {
  flex-shrink: 0; width: 26px; height: 26px; border-radius: 7px; display: grid; place-items: center;
  background: var(--surface-2); font-weight: 700; font-size: .85rem;
}
.opt.selected { border-color: var(--accent); background: var(--accent-soft); }
.opt.correct { border-color: var(--ok); background: var(--ok-soft); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.correct .letter { background: var(--ok); color: #fff; }
.opt.wrong .letter { background: var(--bad); color: #fff; }
.opt:disabled { cursor: default; }
.explain { margin-top: 18px; padding: 16px 18px; border-radius: 10px; background: var(--surface-2); border: 1px solid var(--border); }
.explain.ok { border-color: var(--ok); }
.explain.bad { border-color: var(--bad); }
.explain h4 { margin-bottom: 6px; }
.explain > :last-child { margin-bottom: 0; }
.quiz-bar { display: flex; gap: 12px; align-items: center; margin-bottom: 16px; flex-wrap: wrap; }
.timer { font-family: var(--mono); font-weight: 600; padding: 4px 10px; border-radius: 8px; background: var(--surface-2); }
.timer.low { background: var(--bad-soft); color: var(--bad); }
.qnav { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 18px; }
.qnav button {
  width: 34px; height: 34px; border-radius: 8px; border: 1px solid var(--border); background: var(--surface);
  cursor: pointer; font-size: .8rem; font-weight: 600;
}
.qnav button.answered { background: var(--surface-2); }
.qnav button.flagged { border-color: var(--accent); box-shadow: inset 0 -3px 0 var(--accent); }
.qnav button.current { outline: 2px solid var(--link); }
.qnav button.r-ok { background: var(--ok-soft); color: var(--ok); }
.qnav button.r-bad { background: var(--bad-soft); color: var(--bad); }

.score-ring { width: 160px; height: 160px; margin: 0 auto 10px; position: relative; }
.score-ring svg { transform: rotate(-90deg); }
.score-ring .val { position: absolute; inset: 0; display: grid; place-items: center; font-size: 1.9rem; font-weight: 800; }
.bar-row { display: grid; grid-template-columns: minmax(120px, 1fr) 2fr 52px; gap: 12px; align-items: center; margin: 8px 0; font-size: .9rem; }

/* ---------- Flashcards ---------- */
.flash-stage { perspective: 1200px; max-width: 640px; margin: 0 auto; }
.flash {
  position: relative; height: 300px; cursor: pointer; transition: transform .5s; transform-style: preserve-3d;
}
.flash.flipped { transform: rotateY(180deg); }
.flash .face {
  position: absolute; inset: 0; backface-visibility: hidden; -webkit-backface-visibility: hidden;
  display: flex; flex-direction: column; align-items: center; justify-content: center; text-align: center;
  padding: 28px; border-radius: 16px; border: 1px solid var(--border); background: var(--surface); box-shadow: var(--shadow);
  font-size: 1.15rem; overflow-y: auto;
}
.flash .back { transform: rotateY(180deg); background: var(--accent-soft); font-size: 1rem; }
.flash .hint { position: absolute; bottom: 12px; font-size: .78rem; color: var(--muted); }
.flash-actions { display: flex; gap: 10px; justify-content: center; margin-top: 18px; flex-wrap: wrap; }
.boxes { display: flex; gap: 8px; justify-content: center; margin: 14px 0; flex-wrap: wrap; }
.boxes span { font-size: .8rem; padding: 3px 10px; border-radius: 8px; background: var(--surface-2); }

/* ---------- Forms & tools ---------- */
label.field { display: block; font-weight: 600; font-size: .9rem; margin-bottom: 14px; }
label.field > span { display: block; margin-bottom: 6px; }
input[type="text"], input[type="number"], select {
  width: 100%; padding: 9px 12px; border-radius: 9px; border: 1px solid var(--border); background: var(--surface);
}
input[type="range"] { width: 100%; accent-color: var(--accent); }
.seg { display: inline-flex; max-width: 100%; border: 1px solid var(--border); border-radius: 10px; overflow: hidden; flex-wrap: wrap; }
.seg button { flex: 1 1 auto; border: 0; background: var(--surface); padding: 8px 14px; cursor: pointer; font-size: .88rem; font-weight: 500; }
.chk { display: flex; gap: 8px; align-items: flex-start; margin: 6px 0; font-weight: 500; cursor: pointer; }
.chk input { margin-top: .3em; flex-shrink: 0; accent-color: var(--accent); }
.seg button + button { border-left: 1px solid var(--border); }
.seg button.on { background: var(--accent); color: var(--accent-ink); font-weight: 700; }
.result-box { border: 2px solid var(--accent); border-radius: var(--radius); padding: 18px 20px; background: var(--accent-soft); }
.result-box h3 { margin-bottom: 4px; }
.strategy-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); gap: 12px; }
.strategy { border: 2px solid var(--border); border-radius: 12px; padding: 14px; background: var(--surface); opacity: .6; transition: all .2s; }
.strategy.on { opacity: 1; border-color: var(--accent); box-shadow: var(--shadow); }
.strategy h4 { margin-bottom: 4px; }
.meter { display: flex; gap: 3px; margin: 6px 0; }
.meter i { flex: 1; height: 6px; border-radius: 3px; background: var(--surface-2); }
.meter i.f { background: var(--accent); }
.mono { font-family: var(--mono); }
.subnet-row { font-family: var(--mono); font-size: .85rem; }
.tree-step { border-left: 3px solid var(--accent); padding-left: 14px; margin-bottom: 14px; }
.tool-card { display: flex; flex-direction: column; gap: 6px; color: var(--text); }
.tool-card:hover { text-decoration: none; border-color: var(--accent); }
.tool-card .emoji { font-size: 1.6rem; }

.empty { text-align: center; padding: 40px 20px; color: var(--muted); }
.pad { padding: 24px; }
.footer { margin-top: 60px; padding-top: 20px; border-top: 1px solid var(--border); font-size: .82rem; color: var(--muted); }