:root {
  --bg: #eef2f6;
  --surface: #ffffff;
  --surface-2: #f4f7fa;
  --ink: #13202e;
  --muted: #566577;
  --line: #d3dde6;
  --accent: #0f766e;
  --accent-ink: #ffffff;
  --good: #15803d;
  --good-soft: #dcfce7;
  --bad: #b91c1c;
  --bad-soft: #fee2e2;
  --track: #dde5ec;
  --shadow: 0 1px 2px rgba(16, 32, 48, .06), 0 8px 24px rgba(16, 32, 48, .06);
  --sans: ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", Consolas, monospace;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0c141d; --surface: #131e2b; --surface-2: #0f1925; --ink: #e7eef6; --muted: #92a3b6;
    --line: #243444; --accent: #2dd4bf; --accent-ink: #04201c; --good: #4ade80; --good-soft: #10251a;
    --bad: #f87171; --bad-soft: #2a1414; --track: #24323f;
    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 10px 30px rgba(0,0,0,.35);
  }
}
:root[data-theme="light"] {
  --bg:#eef2f6; --surface:#fff; --surface-2:#f4f7fa; --ink:#13202e; --muted:#566577; --line:#d3dde6;
  --accent:#0f766e; --accent-ink:#fff; --good:#15803d; --good-soft:#dcfce7; --bad:#b91c1c; --bad-soft:#fee2e2; --track:#dde5ec;
  --shadow:0 1px 2px rgba(16,32,48,.06), 0 8px 24px rgba(16,32,48,.06);
}
:root[data-theme="dark"] {
  --bg:#0c141d; --surface:#131e2b; --surface-2:#0f1925; --ink:#e7eef6; --muted:#92a3b6; --line:#243444;
  --accent:#2dd4bf; --accent-ink:#04201c; --good:#4ade80; --good-soft:#10251a; --bad:#f87171; --bad-soft:#2a1414; --track:#24323f;
  --shadow:0 1px 2px rgba(0,0,0,.3), 0 10px 30px rgba(0,0,0,.35);
}

* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--ink); font-family: var(--sans); line-height: 1.5; -webkit-font-smoothing: antialiased; }

.topbar { display: flex; align-items: center; justify-content: space-between; padding: .8rem clamp(1rem, 4vw, 2rem); border-bottom: 1px solid var(--line); background: var(--surface); position: sticky; top: 0; z-index: 5; }
.brand { display: flex; align-items: center; gap: .5rem; font-weight: 700; letter-spacing: -.01em; }
.brand .mark { color: var(--accent); }
.theme-toggle { border: 1px solid var(--line); background: var(--surface-2); color: var(--ink); width: 34px; height: 34px; border-radius: 8px; cursor: pointer; font-size: 1rem; }
.theme-toggle:hover { border-color: var(--accent); }

.container { max-width: 860px; margin: 0 auto; padding: clamp(1.25rem, 4vw, 2.5rem) clamp(1rem, 4vw, 2rem) 4rem; }
.loading { color: var(--muted); }

/* hero / dashboard */
.eyebrow { font-family: var(--mono); font-size: .72rem; letter-spacing: .16em; text-transform: uppercase; color: var(--muted); margin: 0 0 .5rem; }
h1 { font-size: clamp(1.8rem, 4.5vw, 2.6rem); line-height: 1.05; margin: 0 0 .5rem; font-weight: 800; letter-spacing: -.02em; }
.lede { color: var(--muted); margin: 0 0 1.4rem; font-size: 1.05rem; max-width: 60ch; }

.progress-row { display: flex; align-items: center; gap: 1.4rem; flex-wrap: wrap; margin-bottom: 2rem; }
.stat { display: flex; flex-direction: column; }
.stat .n { font-family: var(--mono); font-size: 1.5rem; font-weight: 700; }
.stat .l { font-size: .8rem; color: var(--muted); }

.primary { background: var(--accent); color: var(--accent-ink); border: none; border-radius: 10px; padding: .7rem 1.3rem; font-size: 1rem; font-weight: 650; cursor: pointer; font-family: inherit; }
.primary:hover { filter: brightness(1.06); }
.primary:focus-visible, .option:focus-visible, .ghost:focus-visible { outline: 3px solid color-mix(in srgb, var(--accent) 45%, transparent); outline-offset: 2px; }
.ghost { background: transparent; color: var(--muted); border: 1px solid var(--line); border-radius: 10px; padding: .6rem 1.1rem; font-size: .95rem; cursor: pointer; font-family: inherit; }
.ghost:hover { color: var(--ink); border-color: var(--accent); }

.skills { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: .8rem; }
.skill-card { background: var(--surface); border: 1px solid var(--line); border-radius: 12px; padding: 1rem 1.1rem; box-shadow: var(--shadow); }
.skill-card.locked { opacity: .55; }
.skill-head { display: flex; align-items: center; justify-content: space-between; gap: .5rem; margin-bottom: .3rem; }
.skill-name { font-weight: 700; }
.skill-desc { font-size: .85rem; color: var(--muted); min-height: 2.4em; margin-bottom: .6rem; }
.badge { font-family: var(--mono); font-size: .6rem; letter-spacing: .05em; text-transform: uppercase; font-weight: 700; padding: .2rem .45rem; border-radius: 999px; white-space: nowrap; background: var(--surface-2); color: var(--muted); border: 1px solid var(--line); }
.badge.mastered { background: var(--good-soft); color: var(--good); border-color: transparent; }
.badge.due { background: #fef3c7; color: #92600a; border-color: transparent; }
.badge.learning { background: color-mix(in srgb, var(--accent) 14%, transparent); color: var(--accent); border-color: transparent; }
.bar { height: 8px; border-radius: 999px; background: var(--track); overflow: hidden; }
.bar > span { display: block; height: 100%; background: var(--accent); border-radius: 999px; transition: width .35s ease; }
.skill-card.mastered .bar > span { background: var(--good); }
.bar-label { display: flex; justify-content: space-between; gap: .5rem; font-size: .72rem; color: var(--muted); margin-top: .35rem; }
.prereq { text-align: right; }

.footer-row { display: flex; align-items: center; gap: 1rem; margin-top: 2rem; flex-wrap: wrap; }
.hint { color: var(--muted); font-size: .82rem; }

/* session */
.session { background: var(--surface); border: 1px solid var(--line); border-radius: 16px; padding: clamp(1.2rem, 4vw, 2rem); box-shadow: var(--shadow); }
.session-top { display: flex; align-items: center; justify-content: space-between; margin-bottom: 1rem; }
.skill-tag { font-family: var(--mono); font-size: .72rem; letter-spacing: .06em; text-transform: uppercase; color: var(--accent); font-weight: 700; }
.counter { font-family: var(--mono); font-size: .8rem; color: var(--muted); }
.prompt { font-size: clamp(1.15rem, 2.6vw, 1.5rem); line-height: 1.3; margin: 0 0 1.3rem; font-weight: 700; text-wrap: balance; }

.options { display: grid; gap: .6rem; }
.option { text-align: left; background: var(--surface-2); border: 1.5px solid var(--line); border-radius: 11px; padding: .8rem 1rem; font-size: 1rem; cursor: pointer; color: var(--ink); font-family: inherit; transition: border-color .12s, background .12s; }
.option:hover:not(:disabled) { border-color: var(--accent); }
.option:disabled { cursor: default; }
.option.correct { border-color: var(--good); background: var(--good-soft); font-weight: 650; }
.option.wrong { border-color: var(--bad); background: var(--bad-soft); }

.short-answer { display: flex; gap: .6rem; }
.short-answer input { flex: 1; background: var(--surface-2); border: 1.5px solid var(--line); border-radius: 11px; padding: .8rem 1rem; font-size: 1rem; color: var(--ink); font-family: inherit; }
.short-answer input:focus { outline: none; border-color: var(--accent); }
.short-answer input:disabled { opacity: .7; }

.feedback { margin-top: 1.4rem; border-radius: 12px; padding: 1rem 1.1rem; border: 1px solid var(--line); background: var(--surface-2); }
.feedback.ok { border-left: 4px solid var(--good); }
.feedback.no { border-left: 4px solid var(--bad); }
.fb-head { font-weight: 800; letter-spacing: -.01em; margin-bottom: .3rem; }
.feedback.ok .fb-head { color: var(--good); }
.feedback.no .fb-head { color: var(--bad); }
.fb-answer { font-size: .95rem; margin-bottom: .3rem; }
.fb-explain { color: var(--muted); font-size: .92rem; margin-bottom: .8rem; }
.fb-mastery { font-size: .88rem; font-family: var(--mono); margin-bottom: 1rem; }
.delta { font-weight: 700; }
.delta.up { color: var(--good); }
.delta.down { color: var(--bad); }
.mastered-flag { color: var(--good); font-weight: 700; }

.summary .unlocked { background: var(--good-soft); color: var(--good); border-radius: 10px; padding: .7rem 1rem; margin: 0 0 1.4rem; font-weight: 600; display: inline-block; }
.summary button { margin-right: .6rem; }