/* System Design Lab — palette carried over from the chapter decks, dark-first. */
:root[data-theme="dark"] {
  --bg: #0a0f1e;
  --panel: #101830;
  --panel-2: #16203c;
  --ink: #dce6f7;
  --ink-strong: #f2f7ff;
  --mute: #8ba0c4;
  --line: #23304f;
  --teal: #4ec3e0;
  --deep: #2b8fb8;
  --gold: #F6AE2D;
  --coral: #E5564E;
  --green: #3fbf8f;
  --code-bg: #0d1426;
}
:root[data-theme="light"] {
  --bg: #F5F9FC;
  --panel: #ffffff;
  --panel-2: #eef4fa;
  --ink: #16233d;
  --ink-strong: #0B1B3B;
  --mute: #5a6b88;
  --line: #d3dfec;
  --teal: #1C7293;
  --deep: #065A82;
  --gold: #b8790b;
  --coral: #cc3f37;
  --green: #1d8a63;
  --code-bg: #eef3f9;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.65 -apple-system, "Segoe UI", Roboto, "Helvetica Neue", sans-serif;
}
a { color: var(--teal); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---- chrome ---- */
.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; justify-content: space-between;
  gap: 1rem; padding: .7rem clamp(1rem, 4vw, 2.5rem);
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.topbar-right { display: flex; gap: .4rem; align-items: center; }
.back { color: var(--mute); font-size: .88rem; }
.back:hover { color: var(--teal); text-decoration: none; }
.icon-btn {
  background: var(--panel); color: var(--mute);
  border: 1px solid var(--line); border-radius: 8px;
  width: 2rem; height: 2rem; cursor: pointer; font-size: .9rem; line-height: 1;
}
.icon-btn:hover { color: var(--teal); border-color: var(--teal); }

main { max-width: 47rem; margin: 0 auto; padding: 2.5rem clamp(1rem, 4vw, 2.5rem) 6rem; }
.kicker {
  text-transform: uppercase; letter-spacing: .14em;
  font-size: .7rem; color: var(--mute); margin: 0 0 .5rem;
}
h1 { font-size: clamp(1.8rem, 5vw, 2.4rem); line-height: 1.15; margin: 0 0 .5rem; color: var(--ink-strong); letter-spacing: -.02em; }
.subtitle { color: var(--mute); font-size: 1.05rem; margin: 0 0 1.5rem; }

.chips { display: flex; flex-wrap: wrap; gap: .4rem; margin-bottom: 2rem; }
.chip {
  font-size: .74rem; letter-spacing: .03em; color: var(--mute);
  border: 1px solid var(--line); border-radius: 999px;
  padding: .18rem .65rem; background: var(--panel);
}
.chip.chapter { color: var(--gold); border-color: color-mix(in srgb, var(--gold) 40%, var(--line)); }

/* ---- home ---- */
.progress-card {
  display: flex; align-items: center; gap: 1.4rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 14px; padding: 1.2rem 1.4rem; margin: 0 0 2.5rem;
}
.ring {
  --pct: 0;
  flex: none; width: 74px; height: 74px; border-radius: 50%;
  display: grid; place-items: center;
  background: conic-gradient(var(--teal) calc(var(--pct) * 1%), var(--line) 0);
}
.ring span {
  width: 58px; height: 58px; border-radius: 50%; background: var(--panel);
  display: grid; place-items: center; font-size: .85rem; font-weight: 600; color: var(--ink-strong);
}
.progress-meta p { margin: 0 0 .6rem; color: var(--mute); font-size: .92rem; }
.progress-meta strong { color: var(--ink-strong); }

.btn {
  display: inline-block; cursor: pointer;
  background: var(--panel-2); color: var(--ink);
  border: 1px solid var(--line); border-radius: 9px;
  padding: .45rem .95rem; font-size: .88rem; font-family: inherit;
}
.btn:hover { border-color: var(--teal); color: var(--teal); text-decoration: none; }
.btn.primary { background: var(--teal); color: #06101f; border-color: var(--teal); font-weight: 600; }
.btn.primary:hover { filter: brightness(1.1); color: #06101f; }
.btn.done { background: transparent; color: var(--green); border-color: var(--green); }

.tier { margin: 0 0 2.4rem; }
.tier.is-empty { opacity: .55; }
.tier-head h2 {
  font-size: 1.15rem; margin: 0 0 .2rem; color: var(--ink-strong);
  display: flex; align-items: center; gap: .6rem; font-weight: 600;
}
.tier-num {
  flex: none; width: 1.7rem; height: 1.7rem; border-radius: 7px;
  background: var(--panel-2); border: 1px solid var(--line);
  display: grid; place-items: center; font-size: .8rem; color: var(--teal);
}
.tier-head p { margin: 0 0 .9rem 2.3rem; color: var(--mute); font-size: .87rem; }
.tier-body { display: grid; gap: .45rem; }
.planned { margin: 0 0 0 2.3rem; font-size: .85rem; color: var(--mute); font-style: italic; }

.lesson-row {
  display: flex; align-items: center; gap: .8rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 11px; padding: .8rem 1rem; color: var(--ink);
}
.lesson-row:hover { border-color: var(--teal); text-decoration: none; }
.tick {
  flex: none; width: 1.15rem; height: 1.15rem; border-radius: 50%;
  border: 1.5px solid var(--line);
}
.lesson-row.is-done .tick { background: var(--green); border-color: var(--green); }
.lesson-row.is-done .tick::after {
  content: "✓"; display: block; color: #06101f; font-size: .72rem;
  text-align: center; line-height: 1.05rem; font-weight: 700;
}
.row-main { flex: 1; display: flex; flex-direction: column; }
.row-main strong { font-weight: 600; font-size: .96rem; }
.row-sub { color: var(--mute); font-size: .82rem; }
.row-min { color: var(--mute); font-size: .76rem; white-space: nowrap; }

/* ---- prose ---- */
.prose > *:first-child { margin-top: 0; }
.prose h2 {
  font-size: 1.28rem; margin: 2.6rem 0 .8rem; color: var(--ink-strong);
  padding-bottom: .3rem; border-bottom: 1px solid var(--line); font-weight: 600;
}
.prose h3 { font-size: 1.05rem; margin: 1.8rem 0 .5rem; color: var(--ink-strong); font-weight: 600; }
.prose p, .prose li { color: var(--ink); }
.prose ul, .prose ol { padding-left: 1.3rem; }
.prose li { margin: .3rem 0; }
.prose strong { color: var(--ink-strong); }
.prose code {
  font-family: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  font-size: .87em; background: var(--code-bg); border: 1px solid var(--line);
  border-radius: 5px; padding: .08em .35em;
}
.prose pre {
  background: var(--code-bg); border: 1px solid var(--line); border-radius: 10px;
  padding: .9rem 1.1rem; overflow-x: auto; font-size: .85rem; line-height: 1.5;
}
.prose pre code { background: none; border: 0; padding: 0; }
.prose blockquote {
  margin: 1.2rem 0; padding: .1rem 0 .1rem 1rem;
  border-left: 3px solid var(--line); color: var(--mute);
}
.table-wrap, .prose table { display: block; overflow-x: auto; }
.prose table { width: 100%; border-collapse: collapse; margin: 1.2rem 0; font-size: .89rem; }
.prose th, .prose td { border: 1px solid var(--line); padding: .5rem .7rem; text-align: left; vertical-align: top; }
.prose th { background: var(--panel-2); color: var(--ink-strong); font-weight: 600; }

/* ---- callouts ---- */
.callout {
  --accent: var(--teal);
  margin: 1.5rem 0; padding: .9rem 1.1rem;
  background: var(--panel); border: 1px solid var(--line);
  border-left: 3px solid var(--accent); border-radius: 0 11px 11px 0;
}
.callout > *:last-child { margin-bottom: 0; }
.callout > *:first-child { margin-top: 0; }
.callout-label {
  text-transform: uppercase; letter-spacing: .12em; font-size: .68rem;
  color: var(--accent); margin: 0 0 .4rem; font-weight: 700;
}
.callout.hook { --accent: var(--coral); }
.callout.key { --accent: var(--gold); }
.callout.interview { --accent: var(--green); }
.callout.warn { --accent: var(--coral); }
.callout.note { --accent: var(--mute); }

/* ---- simulators ---- */
.sim {
  margin: 1.8rem 0; padding: 1rem; background: var(--panel);
  border: 1px solid var(--line); border-radius: 13px;
}
.sim figcaption { margin-top: .7rem; font-size: .82rem; color: var(--mute); text-align: center; }
.sim-loading { color: var(--mute); font-size: .85rem; text-align: center; padding: 2rem 0; }
.sim-controls { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin-bottom: .9rem; }
.sim-controls label { font-size: .8rem; color: var(--mute); display: flex; align-items: center; gap: .4rem; }
.sim-controls input[type="range"] { accent-color: var(--teal); }
.sim-stats {
  display: flex; flex-wrap: wrap; gap: 1.2rem; margin-top: .9rem;
  padding-top: .8rem; border-top: 1px solid var(--line); font-size: .82rem;
}
.sim-stat { display: flex; flex-direction: column; }
.sim-stat b { color: var(--ink-strong); font-size: 1.05rem; font-weight: 600; }
.sim-stat span { color: var(--mute); font-size: .72rem; text-transform: uppercase; letter-spacing: .07em; }

/* ---- quiz ---- */
.quiz { margin: 2.6rem 0 0; }
.quiz h2 {
  font-size: 1.28rem; margin: 0 0 1rem; color: var(--ink-strong);
  padding-bottom: .3rem; border-bottom: 1px solid var(--line); font-weight: 600;
}
.qs { list-style: none; padding: 0; margin: 0; display: grid; gap: 1.1rem; }
.q { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 1rem 1.15rem; }
.q-text { margin: 0 0 .7rem; font-weight: 600; color: var(--ink-strong); }
.opts { list-style: none; padding: 0; margin: 0; display: grid; gap: .4rem; }
.opt {
  width: 100%; text-align: left; cursor: pointer; font: inherit; font-size: .92rem;
  background: var(--panel-2); color: var(--ink);
  border: 1px solid var(--line); border-radius: 9px; padding: .5rem .8rem;
}
.opt:hover:not(:disabled) { border-color: var(--teal); }
.opt:disabled { cursor: default; }
.opt.correct { border-color: var(--green); color: var(--green); background: color-mix(in srgb, var(--green) 12%, var(--panel-2)); }
.opt.wrong { border-color: var(--coral); color: var(--coral); background: color-mix(in srgb, var(--coral) 12%, var(--panel-2)); }
.why {
  margin: .7rem 0 0; padding-top: .6rem; border-top: 1px dashed var(--line);
  font-size: .87rem; color: var(--mute);
}
.quiz-score { margin-top: 1rem; font-size: .92rem; color: var(--ink-strong); font-weight: 600; }

/* ---- lesson footer ---- */
.lesson-actions { margin: 2.6rem 0 1.5rem; }
.lesson-nav { display: grid; grid-template-columns: 1fr 1fr; gap: .6rem; }
.nav-card {
  display: flex; flex-direction: column; gap: .2rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 11px; padding: .75rem .95rem; color: var(--ink);
}
.nav-card:hover { border-color: var(--teal); text-decoration: none; }
.nav-card span { font-size: .72rem; color: var(--mute); text-transform: uppercase; letter-spacing: .07em; }
.nav-card strong { font-weight: 600; font-size: .9rem; }
.nav-card.next { text-align: right; }
.nav-card.empty { background: none; border: 0; }

/* ---- top nav ---- */
.topnav { display: flex; gap: .2rem; }
.navlink {
  font-size: .86rem; color: var(--mute); padding: .3rem .7rem;
  border-radius: 8px; border: 1px solid transparent;
}
.navlink:hover { color: var(--teal); text-decoration: none; background: var(--panel); }
.navlink.is-current { color: var(--ink-strong); background: var(--panel); border-color: var(--line); }

/* ---- quick links on the home page ---- */
.quick-links { display: grid; gap: .6rem; grid-template-columns: 1fr 1fr; margin: 0 0 2.5rem; }
.quick {
  display: flex; flex-direction: column; gap: .25rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 12px; padding: .9rem 1.05rem; color: var(--ink);
}
.quick:hover { border-color: var(--teal); text-decoration: none; }
.quick strong { font-size: .95rem; color: var(--ink-strong); font-weight: 600; }
.quick span { font-size: .8rem; color: var(--mute); }
.quick b { color: var(--teal); }
kbd {
  font: inherit; font-size: .74em; background: var(--panel-2); color: var(--ink);
  border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 4px; padding: .05em .3em;
}

/* ---- glossary term links inside prose ---- */
a.term {
  color: var(--ink); text-decoration: none;
  border-bottom: 1px dotted var(--teal); cursor: help;
}
a.term:hover { color: var(--teal); }

/* ---- glossary page ---- */
.alpha { display: flex; flex-wrap: wrap; gap: .3rem; margin: 0 0 2rem; }
.alpha a {
  width: 1.8rem; height: 1.8rem; display: grid; place-items: center;
  border: 1px solid var(--line); border-radius: 7px;
  background: var(--panel); font-size: .8rem; color: var(--mute);
}
.alpha a:hover { border-color: var(--teal); color: var(--teal); text-decoration: none; }
.alpha-group > h2 {
  font-size: 1.5rem; color: var(--teal); margin: 2.2rem 0 .8rem;
  padding-bottom: .2rem; border-bottom: 1px solid var(--line); scroll-margin-top: 4rem;
}
.term-entry {
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 12px; padding: .9rem 1.1rem; margin: 0 0 .6rem; scroll-margin-top: 4.5rem;
}
.term-entry:target { border-color: var(--teal); box-shadow: 0 0 0 2px color-mix(in srgb, var(--teal) 22%, transparent); }
.term-entry h3 { margin: 0 0 .35rem; font-size: 1rem; color: var(--ink-strong); font-weight: 600; }
.term-body p { margin: 0 0 .4rem; font-size: .92rem; }
.term-body > *:last-child { margin-bottom: 0; }
.term-body code {
  font-family: ui-monospace, Menlo, Consolas, monospace; font-size: .85em;
  background: var(--code-bg); border: 1px solid var(--line); border-radius: 4px; padding: .05em .3em;
}
.term-lesson { display: inline-block; margin-top: .45rem; font-size: .78rem; color: var(--mute); }
.term-lesson:hover { color: var(--teal); }

/* ---- drills ---- */
.drill-stats {
  display: flex; flex-wrap: wrap; gap: 1.4rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 12px; padding: .9rem 1.1rem; margin: 0 0 1rem;
}
.drill-filters { display: flex; flex-wrap: wrap; gap: .5rem; align-items: center; margin: 0 0 1.4rem; }
.drill-filters label { font-size: .82rem; color: var(--mute); display: flex; align-items: center; gap: .4rem; }
.drill-filters select {
  font: inherit; font-size: .85rem; background: var(--panel-2); color: var(--ink);
  border: 1px solid var(--line); border-radius: 8px; padding: .35rem .5rem;
}
.drill-card {
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 13px; padding: 1.2rem 1.3rem;
}
.drill-meta { margin: 0 0 .8rem; font-size: .76rem; color: var(--mute); text-transform: uppercase; letter-spacing: .07em; }
.drill-card .q-text { font-size: 1.05rem; margin: 0 0 1rem; }
.drill-answer { border-top: 1px dashed var(--line); margin-top: 1rem; padding-top: .9rem; font-size: .94rem; }
.drill-answer p { margin: 0 0 .6rem; }
.drill-answer > *:last-child { margin-bottom: 0; }
.drill-answer code {
  font-family: ui-monospace, Menlo, Consolas, monospace; font-size: .85em;
  background: var(--code-bg); border: 1px solid var(--line); border-radius: 4px; padding: .05em .3em;
}
.drill-actions { display: flex; gap: .5rem; align-items: center; margin-top: 1rem; }
.drill-next-due { font-size: .8rem; color: var(--mute); margin-right: auto; }
.drill-done { background: var(--panel); border: 1px solid var(--line); border-radius: 13px; padding: 2rem 1.3rem; text-align: center; }
.drill-done h2 { margin: 0 0 .5rem; font-size: 1.2rem; color: var(--ink-strong); }
.drill-done p { margin: 0 0 .3rem; color: var(--mute); }

/* ---- mocks ---- */
.row-score { font-size: .8rem; color: var(--green); font-weight: 600; white-space: nowrap; }
.mock-row .row-sub { text-transform: capitalize; }

.mock-bar {
  position: sticky; top: 3.1rem; z-index: 10;
  display: flex; align-items: center; gap: 1rem;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 12px; padding: .7rem 1rem; margin: 0 0 1rem;
}
.mock-clock { display: flex; align-items: baseline; gap: .4rem; }
.mock-clock b { font-size: 1.35rem; font-weight: 600; color: var(--ink-strong); font-variant-numeric: tabular-nums; }
.mock-clock b.is-over { color: var(--coral); }
.mock-clock span { font-size: .78rem; color: var(--mute); }
.mock-progress { flex: 1; height: .4rem; border-radius: 3px; background: var(--panel-2); overflow: hidden; }
.mock-progress > div { height: 100%; width: 0; background: var(--teal); transition: width .4s linear; }

.mock-stages {
  list-style: none; padding: 0; margin: 0 0 1.4rem;
  display: flex; flex-wrap: wrap; gap: .35rem;
}
.mock-stages li {
  display: flex; align-items: baseline; gap: .4rem;
  font-size: .78rem; color: var(--mute);
  border: 1px solid var(--line); border-radius: 999px; padding: .2rem .7rem;
}
.mock-stages li.is-current { color: var(--ink-strong); border-color: var(--teal); background: var(--panel); }
.mock-stages li.is-done { opacity: .5; }
.mock-stages li.is-done .st-name { text-decoration: line-through; }
.st-min { opacity: .7; font-size: .72rem; }

.mock-stage {
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 13px; padding: 1.1rem 1.3rem; margin: 0 0 1rem;
}
.mock-stage h2 { margin: 0 0 .6rem; font-size: 1.25rem; color: var(--ink-strong); border: 0; padding: 0; }
.mock-ask { margin: 0 0 1rem; font-size: 1rem; }
.mock-probes ul {
  margin: .8rem 0 0; padding-left: 1.2rem; font-size: .89rem; color: var(--mute);
  border-top: 1px dashed var(--line); padding-top: .8rem;
}
.mock-probes li { margin: .3rem 0; }
.mock-nav { display: flex; gap: .5rem; margin-top: 1.1rem; }
.mock-nav .btn:disabled { opacity: .4; cursor: default; }

.mock-pad label {
  display: block; font-size: .76rem; text-transform: uppercase; letter-spacing: .08em;
  color: var(--mute); margin-bottom: .4rem;
}
.mock-pad textarea {
  width: 100%; min-height: 16rem; resize: vertical;
  font-family: ui-monospace, Menlo, Consolas, monospace; font-size: .87rem; line-height: 1.6;
  background: var(--code-bg); color: var(--ink);
  border: 1px solid var(--line); border-radius: 11px; padding: .9rem 1rem;
}
.mock-pad textarea:focus { outline: none; border-color: var(--teal); }

.rubric-group { margin: 0 0 1.4rem; }
.rubric-group h2 {
  font-size: 1.02rem; margin: 0 0 .6rem; color: var(--teal); font-weight: 600;
  border: 0; padding: 0;
}
.rubric { list-style: none; padding: 0; margin: 0; display: grid; gap: .35rem; }
.rubric li {
  background: var(--panel); border: 1px solid var(--line); border-radius: 9px;
}
.rubric label {
  display: flex; gap: .6rem; align-items: flex-start;
  padding: .55rem .8rem; cursor: pointer; font-size: .91rem;
}
.rubric input { margin-top: .25rem; accent-color: var(--teal); flex: none; }
.rubric li:has(input:checked) { border-color: var(--green); }
.rubric li:has(input:checked) span { color: var(--mute); text-decoration: line-through; }

.mock-pct { color: var(--teal); font-size: .6em; }
.mock-answer {
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 13px; padding: .9rem 1.2rem; margin: 1.4rem 0;
}
.mock-answer summary {
  cursor: pointer; font-weight: 600; color: var(--ink-strong); font-size: .95rem;
}
.mock-answer .prose { margin-top: 1rem; }
.mock-answer .prose h2 { font-size: 1.1rem; margin-top: 1.6rem; }
.mock-notes {
  background: var(--code-bg); border: 1px solid var(--line); border-radius: 9px;
  padding: .9rem 1rem; overflow-x: auto; font-size: .85rem; margin-top: 1rem;
  white-space: pre-wrap;
}

/* ---- command palette ---- */
.palette {
  position: fixed; inset: 0; z-index: 100;
  background: rgba(0, 0, 0, .5); backdrop-filter: blur(3px);
  display: flex; justify-content: center; align-items: flex-start; padding: 12vh 1rem 1rem;
}
.palette[hidden] { display: none; }
.palette-box {
  width: min(38rem, 100%); background: var(--panel);
  border: 1px solid var(--line); border-radius: 14px; overflow: hidden;
  box-shadow: 0 20px 60px rgba(0, 0, 0, .45);
}
#palette-input {
  width: 100%; font: inherit; font-size: 1rem; padding: .95rem 1.1rem;
  background: transparent; color: var(--ink); border: 0; border-bottom: 1px solid var(--line);
}
#palette-input:focus { outline: none; }
.palette-results { list-style: none; margin: 0; padding: .35rem; max-height: 22rem; overflow-y: auto; }
.palette-item {
  display: flex; gap: .7rem; align-items: baseline;
  padding: .5rem .7rem; border-radius: 9px; cursor: pointer;
}
.palette-item.is-active { background: var(--panel-2); }
.palette-kind {
  flex: none; font-size: .64rem; text-transform: uppercase; letter-spacing: .09em;
  color: var(--mute); border: 1px solid var(--line); border-radius: 5px;
  padding: .08rem .35rem; width: 3.6rem; text-align: center;
}
.palette-main { display: flex; flex-direction: column; min-width: 0; }
.palette-main strong { font-size: .93rem; font-weight: 600; color: var(--ink-strong); }
.palette-main span {
  font-size: .79rem; color: var(--mute);
  overflow: hidden; text-overflow: ellipsis; white-space: nowrap;
}
.palette-empty { padding: 1rem .8rem; color: var(--mute); font-size: .88rem; }

@media (max-width: 560px) {
  .lesson-nav { grid-template-columns: 1fr; }
  .nav-card.next { text-align: left; }
  .progress-card { flex-direction: column; align-items: flex-start; }
  .quick-links { grid-template-columns: 1fr; }
  .topbar { gap: .4rem; }
  .navlink { padding: .3rem .5rem; font-size: .8rem; }
}