:root {
  --paper: #f3ecdf;
  --paper-2: #e9e0cf;
  --card: #fffaf2;
  --ink: #1a1714;
  --ink-soft: #3c362f;
  --muted: #6e665c;
  --line: #d8cdb8;
  --seal: #c2412d;
  --seal-deep: #8d2e1d;
  --pine: #1c4a42;
  --pine-mid: #2c6b60;
  --gold: #a56b1f;
  --shadow: 0 16px 40px rgba(48, 32, 12, 0.08);
  --serif: "Newsreader", "Iowan Old Style", Georgia, serif;
  --sans: "Outfit", "Avenir Next", "Segoe UI", sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, monospace;
  --max: 1080px;
  --pad: clamp(1.1rem, 3vw, 2rem);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 5.25rem; }
body {
  margin: 0;
  color: var(--ink);
  background:
    radial-gradient(1200px 500px at 10% -10%, rgba(194, 65, 45, 0.08), transparent 50%),
    radial-gradient(900px 400px at 110% 0%, rgba(28, 74, 66, 0.08), transparent 46%),
    var(--paper);
  font-family: var(--sans);
  font-size: 1.05rem;
  line-height: 1.55;
  font-weight: 400;
}
body::before {
  content: "";
  position: fixed;
  inset: 0 auto 0 0;
  width: 28px;
  background:
    linear-gradient(var(--seal), var(--seal)) 10px 0 / 1px 100% no-repeat,
    #ead9c6;
  z-index: 20;
  pointer-events: none;
}
img { max-width: 100%; }
a { color: var(--seal-deep); }
a:hover { color: var(--seal); }
:focus-visible {
  outline: 2px solid var(--pine);
  outline-offset: 3px;
}
::selection { background: #f0c2a4; }

.skip {
  position: absolute;
  left: 2.5rem;
  top: -4rem;
  background: var(--ink);
  color: var(--paper);
  padding: 0.4rem 0.7rem;
  z-index: 30;
}
.skip:focus { top: 0.6rem; }

.top {
  position: sticky;
  top: 0;
  z-index: 15;
  display: flex;
  align-items: center;
  gap: 1rem;
  padding: 0.75rem var(--pad) 0.75rem calc(var(--pad) + 18px);
  background: rgba(243, 236, 223, 0.9);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}
.mark {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  text-decoration: none;
  color: inherit;
  margin-right: auto;
}
.mark strong {
  display: block;
  font-family: var(--serif);
  font-size: 1.35rem;
  font-weight: 560;
  letter-spacing: -0.03em;
  line-height: 1;
}
.mark em {
  display: block;
  font-style: normal;
  font-family: var(--mono);
  font-size: 0.68rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}
.seal {
  width: 2.1rem;
  height: 2.1rem;
  display: grid;
  place-items: center;
  background: var(--ink);
  color: var(--paper);
  font-family: var(--serif);
  font-weight: 560;
  border-radius: 4px;
}
.nav { display: flex; gap: 0.15rem; flex-wrap: wrap; }
.nav a {
  text-decoration: none;
  color: var(--ink-soft);
  padding: 0.35rem 0.6rem;
  border-radius: 999px;
  font-size: 0.92rem;
}
.nav a:hover { background: rgba(26, 23, 20, 0.05); color: var(--ink); }
.nav a[aria-current="page"] {
  background: var(--ink);
  color: var(--paper);
}
.progress-pill {
  text-decoration: none;
  font-family: var(--mono);
  font-size: 0.75rem;
  letter-spacing: 0.04em;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--pine);
  padding: 0.35rem 0.6rem;
  border-radius: 999px;
  white-space: nowrap;
}
.nav-toggle { display: none; }

main {
  width: min(var(--max), calc(100% - 36px));
  margin: 0 auto;
  padding: 2.2rem var(--pad) 4rem;
  outline: none;
}
.colophon {
  width: min(var(--max), calc(100% - 36px));
  margin: 0 auto;
  padding: 0 var(--pad) 2.5rem calc(var(--pad));
  color: var(--muted);
  font-size: 0.88rem;
}
.noscript {
  margin: 1rem 3rem;
  padding: 1rem;
  background: #fff;
}

.kicker {
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--seal);
  margin: 0 0 0.6rem;
}
h1, h2, h3, h4 { font-family: var(--serif); font-weight: 560; letter-spacing: -0.03em; line-height: 1.08; }
h1 { font-size: clamp(2.6rem, 6vw, 5.1rem); margin: 0 0 0.8rem; }
h2 { font-size: clamp(1.7rem, 3vw, 2.3rem); margin: 2rem 0 0.6rem; }
h3 { font-size: 1.35rem; margin: 0 0 0.4rem; }
.lede {
  font-family: var(--serif);
  font-size: clamp(1.25rem, 2vw, 1.55rem);
  line-height: 1.35;
  max-width: 38rem;
  margin: 0 0 1.4rem;
  color: var(--ink-soft);
}
.hero-actions, .row { display: flex; flex-wrap: wrap; gap: 0.7rem; align-items: center; }
.lesson-top, .btn, button, .quiz-choices button, h1 { scroll-margin-top: 5.25rem; }
.btn, button.btn {
  appearance: none;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font-family: var(--sans);
  font-size: 0.95rem;
  padding: 0.65rem 0.95rem;
  border-radius: 999px;
  text-decoration: none;
  cursor: pointer;
}
.btn.ghost, a.btn.ghost {
  background: transparent;
  color: var(--ink);
}
.btn.small { padding: 0.4rem 0.75rem; font-size: 0.85rem; }
.btn:hover { background: var(--seal-deep); border-color: var(--seal-deep); color: #fff; }
.btn.ghost:hover { background: var(--ink); color: var(--paper); }
.btn:disabled { opacity: 0.45; cursor: not-allowed; }

.stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 0.7rem;
  margin: 1.8rem 0 2.4rem;
}
.stat {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 0.9rem 1rem;
  box-shadow: var(--shadow);
}
.stat b {
  display: block;
  font-family: var(--serif);
  font-size: 1.7rem;
  font-weight: 560;
}
.stat span { color: var(--muted); font-size: 0.88rem; }

.section-head {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: end;
  margin-top: 1rem;
}
.section-head p { margin: 0; color: var(--muted); max-width: 28rem; }

.spine { display: grid; gap: 0; margin-top: 0.6rem; }
.station {
  display: grid;
  grid-template-columns: 4.2rem 1fr auto;
  gap: 0.8rem;
  align-items: center;
  text-decoration: none;
  color: inherit;
  padding: 0.85rem 0;
  border-top: 1px solid var(--line);
}
.station:hover h3 { color: var(--seal-deep); }
.station .num {
  font-family: var(--mono);
  color: var(--muted);
  font-size: 0.85rem;
}
.station p { margin: 0.15rem 0 0; color: var(--muted); font-size: 0.92rem; }
.station .meta { font-family: var(--mono); font-size: 0.72rem; color: var(--pine); letter-spacing: 0.04em; }
.done-dot {
  width: 0.55rem;
  height: 0.55rem;
  border-radius: 50%;
  border: 1.5px solid var(--pine);
  display: inline-block;
  margin-right: 0.35rem;
}
.done-dot.on { background: var(--pine); }

.path-switch { display: flex; gap: 0.5rem; margin: 1rem 0 1.2rem; flex-wrap: wrap; }
.path-switch button {
  font-family: var(--sans);
  border: 1px solid var(--line);
  background: transparent;
  padding: 0.7rem 0.9rem;
  cursor: pointer;
  text-align: left;
  min-width: 9rem;
  border-radius: 8px;
}
.path-switch button strong { display: block; font-family: var(--serif); font-size: 1.2rem; }
.path-switch button span { color: var(--muted); font-size: 0.82rem; }
.path-switch button[aria-pressed="true"] {
  background: var(--ink);
  color: var(--paper);
  border-color: var(--ink);
}
.path-switch button[aria-pressed="true"] span { color: #d9d0c2; }

.checklist { list-style: none; padding: 0; margin: 0; }
.checklist li {
  display: flex;
  gap: 0.75rem;
  align-items: flex-start;
  padding: 0.75rem 0;
  border-bottom: 1px solid var(--line);
}
.checklist a { font-weight: 500; }
.checklist .tag {
  margin-left: auto;
  font-family: var(--mono);
  font-size: 0.7rem;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}

.check {
  width: 1.15rem;
  height: 1.15rem;
  margin-top: 0.2rem;
  accent-color: var(--pine);
}

.prose { max-width: 42rem; }
.prose p { margin: 0.7rem 0; }
.prose ul, .prose ol { margin: 0.4rem 0 0.8rem; padding-left: 1.2rem; }
.prose li { margin: 0.25rem 0; }
.lesson-top {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: end;
  margin-bottom: 0.4rem;
}
.crumbs { color: var(--muted); font-size: 0.9rem; margin-bottom: 0.6rem; }
.crumbs a { color: var(--muted); }

.say, .callout, .card, .panel {
  background: var(--card);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.say, .callout {
  padding: 0.95rem 1.05rem;
  margin: 1rem 0 1.2rem;
  max-width: 42rem;
}
.say { border-left: 3px solid var(--seal); }
.callout { border-left: 3px solid var(--pine); }
.say p, .callout p { margin: 0.3rem 0 0; }

.diagram {
  margin: 1.2rem 0 1.4rem;
  padding: 1rem;
  background: #f7f1e6;
  border: 1px dashed #c9bba3;
  max-width: 46rem;
}
.diagram figcaption {
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.75rem;
}
.lane, .vlane {
  display: flex;
  flex-wrap: wrap;
  gap: 0.85rem 1.15rem;
  align-items: stretch;
}
.vlane { flex-direction: column; align-items: flex-start; }
.box {
  background: var(--card);
  border: 1px solid var(--ink);
  padding: 0.55rem 0.7rem;
  min-width: 6.5rem;
  position: relative;
}
.box b { display: block; font-size: 0.95rem; }
.box span { display: block; color: var(--muted); font-size: 0.78rem; }
.box.pine { background: var(--pine); color: #f3ecdf; border-color: var(--pine); }
.box.pine span { color: #d5ebe6; }
.box.seal { background: var(--seal); color: #fffaf2; border-color: var(--seal); }
.box.seal span { color: #ffd9d1; }
.lane .box:not(:last-child)::after,
.vlane .box:not(:last-child)::after {
  content: "→";
  position: absolute;
  right: -0.72rem;
  top: 50%;
  transform: translateY(-50%);
  color: var(--muted);
  font-size: 0.8rem;
}
.vlane .box:not(:last-child)::after {
  content: "↓";
  right: auto;
  left: 0.7rem;
  top: auto;
  bottom: -0.85rem;
}

.split {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.8rem;
  margin: 1rem 0;
  max-width: 46rem;
}
.split article, .grid-cards article, .choice {
  background: var(--card);
  border: 1px solid var(--line);
  padding: 0.9rem 1rem;
}
.split article p, .grid-cards p { margin: 0.35rem 0 0; color: var(--ink-soft); }

.table-wrap { overflow-x: auto; margin: 1rem 0; max-width: 48rem; }
table {
  width: 100%;
  border-collapse: collapse;
  background: var(--card);
  font-size: 0.95rem;
}
th, td { text-align: left; padding: 0.55rem 0.7rem; border-bottom: 1px solid var(--line); vertical-align: top; }
th { font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); font-weight: 500; }
code, .mono { font-family: var(--mono); font-size: 0.86em; }
pre {
  background: var(--ink);
  color: #f3ecdf;
  padding: 0.9rem 1rem;
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 0.82rem;
  line-height: 1.5;
  max-width: 42rem;
}

.quiz { margin: 1.4rem 0; max-width: 42rem; }
.quiz-choices { display: grid; gap: 0.45rem; margin-top: 0.6rem; }
.quiz-choices button {
  text-align: left;
  font-family: var(--sans);
  font-size: 1rem;
  background: var(--card);
  border: 1px solid var(--line);
  padding: 0.65rem 0.75rem;
  cursor: pointer;
}
.quiz-choices button:hover { border-color: var(--ink); }
.quiz-choices button.good { background: #e5f2ea; border-color: var(--pine); }
.quiz-choices button.bad { background: #fbe8e3; border-color: var(--seal); }
.quiz-why { margin-top: 0.7rem; color: var(--ink-soft); }

.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--line);
  max-width: 46rem;
}
.pager a { text-decoration: none; color: inherit; max-width: 46%; }
.pager small { display: block; color: var(--muted); font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.08em; text-transform: uppercase; }
.pager strong { font-family: var(--serif); font-weight: 560; }

.filters { display: flex; gap: 0.5rem; flex-wrap: wrap; margin: 0.8rem 0 1rem; }
.filters button, .chip {
  border: 1px solid var(--line);
  background: transparent;
  font-family: var(--sans);
  padding: 0.3rem 0.65rem;
  border-radius: 999px;
  cursor: pointer;
  color: var(--ink-soft);
}
.filters button[aria-pressed="true"] { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.search {
  width: min(100%, 22rem);
  border: 1px solid var(--line);
  background: var(--card);
  font-family: var(--sans);
  font-size: 1rem;
  padding: 0.55rem 0.7rem;
  margin-bottom: 0.4rem;
}

.grid-cards {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.8rem;
}
.grid-cards a { text-decoration: none; color: inherit; }
.grid-cards article:hover { border-color: var(--ink); }
.grid-cards .meta { font-family: var(--mono); font-size: 0.72rem; color: var(--pine); letter-spacing: 0.05em; text-transform: uppercase; }

.steps { display: grid; gap: 0.7rem; margin-top: 1rem; }
.step {
  border: 1px solid var(--line);
  background: var(--card);
  padding: 0.9rem 1rem;
}
.step header { display: flex; justify-content: space-between; gap: 1rem; align-items: baseline; }
.step .n {
  font-family: var(--mono);
  color: var(--seal);
  font-size: 0.75rem;
  letter-spacing: 0.08em;
}
.locked { color: var(--muted); }

.stage {
  perspective: 1200px;
  max-width: 36rem;
  margin: 1rem 0;
}
.flip {
  min-height: 16rem;
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.45s ease;
  cursor: pointer;
}
.flip.on { transform: rotateY(180deg); }
.face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  background: var(--card);
  border: 1px solid var(--ink);
  padding: 1.3rem 1.3rem 1.5rem;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  justify-content: space-between;
}
.face.back { transform: rotateY(180deg); background: var(--pine); color: #f4efe4; }
.face p { font-family: var(--serif); font-size: 1.55rem; line-height: 1.25; margin: 0.4rem 0 0; }
.face .hint { font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--muted); }
.face.back .hint { color: #c9e4de; }

.bars { display: grid; gap: 0.45rem; margin: 1rem 0 1.4rem; }
.bar-row { display: grid; grid-template-columns: 14rem 1fr 6.5rem; gap: 0.6rem; align-items: center; font-size: 0.88rem; }
.track { background: #e4d9c6; height: 0.7rem; }
.fill { height: 100%; background: var(--pine); }
.fill.hot { background: var(--seal); }
.bar-row .val { font-family: var(--mono); font-size: 0.75rem; color: var(--muted); text-align: right; }

.form-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0.7rem;
  margin: 0.6rem 0 1rem;
}
label { display: grid; gap: 0.25rem; font-size: 0.88rem; color: var(--muted); }
input[type="number"], input[type="range"] {
  font-family: var(--mono);
  font-size: 1rem;
  padding: 0.45rem 0.5rem;
  border: 1px solid var(--line);
  background: var(--card);
  color: var(--ink);
  width: 100%;
}
.results {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.6rem;
}
.results div {
  background: var(--ink);
  color: var(--paper);
  padding: 0.75rem 0.8rem;
}
.results b { display: block; font-family: var(--serif); font-size: 1.35rem; font-weight: 560; }
.results span { color: #cfc6b6; font-size: 0.78rem; }

.tools {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 1rem;
}
.panel { padding: 1rem; }
.panel h2 { margin-top: 0; }

.library-group { margin: 1.4rem 0; }
.library-group h2 { margin-bottom: 0.3rem; }
.link-list { list-style: none; padding: 0; margin: 0; }
.link-list li { padding: 0.65rem 0; border-bottom: 1px solid var(--line); }
.link-list p { margin: 0.15rem 0 0; color: var(--muted); font-size: 0.92rem; }

@media (max-width: 860px) {
  body::before { display: none; }
  .top { padding-left: var(--pad); }
  main, .colophon { width: min(100% - 0px, 100%); }
  .split, .tools, .results, .form-grid { grid-template-columns: 1fr; }
  .stats, .grid-cards { grid-template-columns: 1fr 1fr; }
  .bar-row { grid-template-columns: 1fr; gap: 0.15rem; }
  .nav-toggle { display: inline-flex; margin-left: auto; }
  .nav {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--paper);
    border-bottom: 1px solid var(--line);
    padding: 0.5rem;
  }
  .nav.open { display: flex; }
  .progress-pill { margin-left: 0; }
  .station { grid-template-columns: 3rem 1fr; }
  .station .meta { grid-column: 2; }
}
@media (max-width: 560px) {
  .stats, .grid-cards { grid-template-columns: 1fr; }
}
@media (prefers-reduced-motion: reduce) {
  .flip { transition: none; }
  html { scroll-behavior: auto; }
}