:root {
  --bg: #f7f5f0;
  --surface: #ffffff;
  --surface-2: #efece4;
  --text: #1d1c1a;
  --muted: #6b675f;
  --border: #e2ddd2;
  --accent: #c2550f;
  --accent-soft: #fbe9dc;
  --good: #1f7a4d;
  --good-soft: #e1f3e8;
  --bad: #b3261e;
  --bad-soft: #fbe4e2;
  --code-bg: #f1eee7;
  --radius: 14px;
  --measure: 40rem;
  --font: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", Roboto, sans-serif;
  --serif: "Iowan Old Style", "Palatino", Georgia, serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16171a;
    --surface: #1f2024;
    --surface-2: #26282d;
    --text: #ecebe8;
    --muted: #a19d95;
    --border: #33353b;
    --accent: #f29a5c;
    --accent-soft: #3a2a1f;
    --good: #6fd09b;
    --good-soft: #1b3226;
    --bad: #f28b82;
    --bad-soft: #3b2120;
    --code-bg: #24262b;
  }
}

* { box-sizing: border-box; }

html { -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 17px/1.6 var(--font);
  min-height: 100vh;
  padding-bottom: env(safe-area-inset-bottom);
}

a { color: var(--accent); }

/* Top bar */
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  gap: 4px;
  padding: calc(env(safe-area-inset-top) + 10px) 16px 10px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  -webkit-backdrop-filter: blur(12px);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.back {
  display: grid;
  place-items: center;
  width: 36px;
  height: 36px;
  margin-left: -8px;
  border-radius: 10px;
  color: var(--text);
}
.back:active { background: var(--surface-2); }
.back[hidden] { display: none; }
.crumb {
  font-weight: 600;
  font-size: 16px;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}
.progress-rail {
  position: sticky;
  top: calc(env(safe-area-inset-top) + 57px);
  z-index: 9;
  height: 3px;
  background: transparent;
}
.progress-bar { height: 100%; width: 0; background: var(--accent); transition: width .1s linear; }

main {
  max-width: var(--measure);
  margin: 0 auto;
  padding: 20px 16px 40px;
  outline: none;
}

.foot {
  max-width: var(--measure);
  margin: 0 auto;
  padding: 0 16px 32px;
  color: var(--muted);
  font-size: 13px;
  text-align: center;
}

/* Home + topic lists */
.hello h1 { font: 700 30px/1.15 var(--font); margin: 8px 0 6px; letter-spacing: -0.02em; }
.hello p { color: var(--muted); margin: 0 0 24px; }

.section-label {
  font-size: 13px;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--muted);
  margin: 28px 0 10px;
}

.card {
  display: block;
  text-decoration: none;
  color: inherit;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  margin-bottom: 12px;
}
.card:active { transform: scale(.99); }
.card h2, .card h3 { margin: 0 0 4px; font-size: 19px; line-height: 1.3; }
.card p { margin: 0; color: var(--muted); font-size: 15px; }
.card .meta { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 10px; font-size: 13px; color: var(--muted); }

.resume { border-color: var(--accent); background: var(--accent-soft); }
.resume .eyebrow { font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--accent); }

.meter { height: 6px; border-radius: 99px; background: var(--surface-2); overflow: hidden; margin-top: 12px; }
.meter > span { display: block; height: 100%; background: var(--accent); border-radius: 99px; }

.lesson-row { display: flex; gap: 14px; align-items: flex-start; }
.lesson-num {
  flex: none;
  width: 32px;
  height: 32px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  font-weight: 700;
  font-size: 14px;
  background: var(--surface-2);
  color: var(--muted);
}
.lesson-num.done { background: var(--good-soft); color: var(--good); }
.pill { padding: 1px 8px; border-radius: 99px; background: var(--surface-2); }
.pill.good { background: var(--good-soft); color: var(--good); }

.topic-head h1 { font: 700 28px/1.2 var(--font); margin: 6px 0 8px; letter-spacing: -0.02em; }
.topic-head p { color: var(--muted); margin: 0 0 8px; }

/* Lesson article */
.lesson-head .eyebrow { font-size: 13px; color: var(--muted); }
.lesson-head h1 { font: 700 28px/1.2 var(--font); margin: 6px 0 4px; letter-spacing: -0.02em; }
.lesson-head .lede { font-family: var(--serif); font-size: 19px; color: var(--muted); margin: 8px 0 20px; }

article { font-family: var(--serif); font-size: 18.5px; line-height: 1.65; }
article h2 { font: 700 22px/1.3 var(--font); margin: 36px 0 10px; letter-spacing: -0.01em; }
article h3 { font: 650 18px/1.35 var(--font); margin: 26px 0 8px; }
article p, article ul, article ol { margin: 0 0 16px; }
article li { margin-bottom: 6px; }
article strong { font-weight: 700; }
article code {
  font: 0.82em/1.4 var(--mono);
  background: var(--code-bg);
  padding: 2px 5px;
  border-radius: 5px;
  overflow-wrap: anywhere;
}
article pre {
  font: 13.5px/1.5 var(--mono);
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 14px;
  overflow-x: auto;
  margin: 0 0 18px;
  -webkit-overflow-scrolling: touch;
}
article pre code { background: none; padding: 0; font-size: inherit; overflow-wrap: normal; }

.callout {
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.55;
  border-radius: 12px;
  padding: 12px 14px;
  margin: 0 0 18px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
}
.callout > :last-child { margin-bottom: 0; }
.callout .label { display: block; font-weight: 700; font-size: 12px; text-transform: uppercase; letter-spacing: .06em; color: var(--accent); margin-bottom: 4px; }
.callout.warn { border-left-color: var(--bad); }
.callout.warn .label { color: var(--bad); }
.callout.key { border-left-color: var(--good); }
.callout.key .label { color: var(--good); }

.table-wrap { overflow-x: auto; margin: 0 0 18px; -webkit-overflow-scrolling: touch; }
article table { border-collapse: collapse; font: 14.5px/1.45 var(--font); min-width: 100%; }
article th, article td { text-align: left; vertical-align: top; padding: 8px 10px; border-bottom: 1px solid var(--border); }
article th { font-weight: 650; background: var(--surface-2); }

/* Simple stacked flow diagram */
.flow { font-family: var(--font); font-size: 15px; margin: 0 0 20px; padding: 0; list-style: none; }
.flow li {
  position: relative;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 12px;
  margin: 0 0 22px;
}
.flow li:not(:last-child)::after {
  content: "↓";
  position: absolute;
  left: 0;
  right: 0;
  bottom: -22px;
  text-align: center;
  font-size: 15px;
  line-height: 22px;
  color: var(--muted);
}
.flow b { display: block; }
.flow span { color: var(--muted); font-size: 14px; }

/* Grid of service tiles */
.tiles { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 8px; margin: 0 0 20px; font-family: var(--font); }
.tiles div { background: var(--surface); border: 1px solid var(--border); border-radius: 10px; padding: 10px; font-size: 14px; line-height: 1.4; }
.tiles b { display: block; font-size: 15px; margin-bottom: 2px; }
.tiles span { color: var(--muted); }

details {
  font-family: var(--font);
  font-size: 16px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 10px 14px;
  margin: 0 0 18px;
}
details summary { font-weight: 600; cursor: pointer; }
details[open] summary { margin-bottom: 8px; }

/* Quiz */
.quiz { margin-top: 40px; padding-top: 24px; border-top: 2px solid var(--border); }
.quiz h2 { font: 700 24px/1.25 var(--font); margin: 0 0 4px; }
.quiz .sub { color: var(--muted); margin: 0 0 20px; font-size: 15px; }
.q { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 16px; margin-bottom: 14px; }
.q-num { font-size: 12px; font-weight: 700; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); }
.q-text { font-weight: 600; margin: 4px 0 12px; line-height: 1.45; }
.opt {
  display: block;
  width: 100%;
  text-align: left;
  font: inherit;
  font-size: 16px;
  line-height: 1.4;
  color: var(--text);
  background: var(--bg);
  border: 1.5px solid var(--border);
  border-radius: 10px;
  padding: 11px 12px;
  margin-bottom: 8px;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
}
.opt:disabled { cursor: default; color: var(--text); }
.opt.correct { border-color: var(--good); background: var(--good-soft); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.dim { opacity: .55; }
.explain { font-size: 15px; line-height: 1.5; margin-top: 6px; padding: 10px 12px; border-radius: 10px; background: var(--surface-2); }
.explain b.good { color: var(--good); }
.explain b.bad { color: var(--bad); }

.score {
  text-align: center;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 16px;
  margin-top: 18px;
}
.score .big { font: 800 40px/1 var(--font); }
.score p { margin: 8px 0 14px; color: var(--muted); }

.btn-row { display: flex; gap: 10px; flex-wrap: wrap; justify-content: center; }
.btn {
  appearance: none;
  display: inline-block;
  font: 600 16px/1 var(--font);
  text-decoration: none;
  padding: 13px 18px;
  border-radius: 12px;
  border: 1.5px solid var(--border);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
@media (prefers-color-scheme: dark) { .btn.primary { color: #1a1206; } }

.next-up { margin-top: 28px; }

.empty { color: var(--muted); text-align: center; padding: 40px 0; }

.lock { display: flex; flex-direction: column; align-items: center; gap: 12px; padding: 64px 0; }
.lock label { color: var(--muted); }
.lock input {
  font: inherit; font-size: 1.6rem; letter-spacing: 0.4em; text-align: center;
  width: 9rem; padding: 10px 12px; border-radius: var(--radius);
  border: 1px solid var(--border); background: var(--surface); color: var(--text);
}
.lock input:focus { outline: 2px solid var(--accent); outline-offset: 2px; }
.lock-msg { color: var(--bad); min-height: 1.4em; margin: 0; }