/*
 * Chess Path styles, built on the Shift Nudge style system (see DESIGN.md for every decision).
 * Quiet greys do the interface; colour lives in the board, the shape band and the stage hues.
 */

/* ------------------------------------------------------------------ tokens */
:root {
  /* Roles (dark is the reference; light swaps the values below) */
  --canvas: #0e0e0e;
  --raised: #181818;
  --raised-2: #1e1e1e;
  --content: #c9c9c9;
  --content-strong: #e5e5e5;
  --content-secondary: #858585; /* 5.1:1 on canvas, 4.8:1 on raised (SN #7C7C7C fails on raised) */
  --content-tertiary: #5f5f5f; /* 3:1: decoration only, never text that matters */
  --border: #1a1a1a;
  --border-strong: #303030;
  --primary: #c9c9c9;
  --primary-hover: #e5e5e5;
  --on-primary: #0e0e0e;
  --interactive: #5bac7b; /* muted jade, not Shift Nudge's red: red means "wrong" here */
  --good: #5bac7b;
  --bad: #dd8384;

  /* Board: muted olive, the one coloured object in the interface */
  --sq-light: #d6cfbc;
  --sq-dark: #9b885c;
  --coord-on-light: #5e5234;
  --coord-on-dark: #231e14;
  --hl-last: rgba(205, 143, 80, 0.5); /* amber */
  --hl-select: rgba(91, 172, 123, 0.55); /* jade */
  --hl-mark: rgba(92, 162, 219, 0.5); /* cobalt */
  --hl-hint: rgba(92, 162, 219, 0.95);
  --hl-check: 221, 131, 132; /* red, as rgb triplet */
  --hl-good: rgba(91, 172, 123, 0.6);
  --hl-bad: rgba(221, 131, 132, 0.7);

  /* Stage hues, jade to violet (text-safe: AAA on dark canvas) */
  --hue-0: #5bac7b;
  --hue-1: #3ead98;
  --hue-2: #41acb2;
  --hue-3: #3ea8c8;
  --hue-4: #5ca2db;
  --hue-5: #809be3;
  --hue-6: #9f94e1;

  /* The 16-hue muted spectrum for illustration (dark: AAA set) */
  --s-red: #dd8384;
  --s-copper: #d98868;
  --s-amber: #cd8f50;
  --s-olive: #ba9844;
  --s-moss: #9ea14a;
  --s-green: #7fa85f;
  --s-jade: #5bac7b;
  --s-teal: #3ead98;
  --s-ocean: #41acb2;
  --s-azure: #3ea8c8;
  --s-cobalt: #5ca2db;
  --s-blue: #809be3;
  --s-violet: #9f94e1;
  --s-purple: #b98dd3;
  --s-magenta: #cb86bc;
  --s-rose: #d783a0;

  /* Type */
  --font:
    "Geist", ui-sans-serif, -apple-system, "Segoe UI", Roboto, Helvetica, Arial,
    sans-serif;
  --mono: "Geist Mono", ui-monospace, "SF Mono", Menlo, Consolas, monospace;
  --text-sm: 14px;
  --text-body: 17px;
  --text-lg: 22px;
  --text-hero: clamp(32px, 4.2vw, 44px);
  --text-display: clamp(32px, 4vw, 44px);

  /* Shape and motion */
  --radius: 4px;
  --radius-panel: 12px;
  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --fade: 150ms var(--ease);

  color-scheme: dark;
}
@media (prefers-color-scheme: light) {
  :root {
    --canvas: #f0f0f0;
    --raised: #f7f7f7;
    --raised-2: #ffffff;
    --content: #0e0e0e;
    --content-strong: #000000;
    --content-secondary: #595959;
    --content-tertiary: #8a8a8a;
    --border: #e5e5e5;
    --border-strong: #cccccc;
    --primary: #1e1e1e;
    --primary-hover: #000000;
    --on-primary: #f0f0f0;
    --interactive: #49735a; /* SN AA jade nudged darker: 4.4 → 4.7:1 */
    --good: #49735a;
    --bad: #a35153;
    --coord-on-light: #5e5234;
    --hue-0: #49735a;
    --hue-1: #48706a;
    --hue-2: #41707a;
    --hue-3: #3f6c86;
    --hue-4: #476e8d;
    --hue-5: #5562a6;
    --hue-6: #6f5bb8;
    /* Illustration uses the brighter light-mode set: it is never text */
    --s-red: #cb6769;
    --s-copper: #ba765b;
    --s-amber: #a8815b;
    --s-olive: #9b885c;
    --s-moss: #8c8e5c;
    --s-green: #75955d;
    --s-jade: #629875;
    --s-teal: #629689;
    --s-ocean: #629497;
    --s-azure: #6192a4;
    --s-cobalt: #608fb7;
    --s-blue: #7087c6;
    --s-violet: #897ec6;
    --s-purple: #a66ec6;
    --s-magenta: #bc66ab;
    --s-rose: #c6668a;
    color-scheme: light;
  }
}

/* ------------------------------------------------------------------ base */
* {
  box-sizing: border-box;
}
html,
body {
  margin: 0;
}
html {
  scroll-behavior: smooth;
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}
body {
  background: var(--canvas);
  color: var(--content);
  font: 400 var(--text-body)/1.55 var(--font);
  letter-spacing: -0.01em;
  -webkit-font-smoothing: antialiased;
  font-feature-settings: "ss01" on;
}
::selection {
  background: color-mix(in srgb, var(--interactive) 30%, transparent);
}
a {
  color: var(--interactive);
  text-underline-offset: 3px;
  text-decoration-thickness: 1px;
}
strong {
  font-weight: 500;
  color: var(--content-strong);
}
button,
select,
input,
textarea {
  font: inherit;
  color: inherit;
  letter-spacing: inherit;
}
:focus-visible {
  outline: 2px solid var(--interactive);
  outline-offset: 2px;
}
/* Inside scrolling containers an outer outline gets clipped, so draw it inside. */
.nav a:focus-visible,
.movelist .mv:focus-visible {
  outline-offset: -2px;
}
.muted {
  color: var(--content-secondary);
}
.small {
  font-size: 13px;
}
.dim {
  color: var(--content-secondary);
}

/* Tags: Geist Mono, sentence case, small. */
.tag {
  display: inline-flex;
  align-items: center;
  font: 500 11px/1 var(--mono);
  padding: 4px 6px;
  border-radius: var(--radius);
  background: color-mix(in srgb, currentColor 14%, transparent);
  color: var(--content-secondary);
  white-space: nowrap;
}

/* ------------------------------------------------------------------ header */
.top {
  position: sticky;
  top: 0;
  z-index: 10;
  height: 58px;
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 0 20px;
  background: color-mix(in srgb, var(--canvas) 85%, transparent);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}
.brand {
  font-weight: 500;
  font-size: 15px;
  color: var(--content);
  text-decoration: none;
  display: flex;
  align-items: center;
  gap: 8px;
  white-space: nowrap;
}
.logo {
  font-size: 22px;
  line-height: 1;
  font-family:
    "Apple Symbols", "Segoe UI Symbol", "DejaVu Sans", "Noto Sans Symbols 2",
    serif;
}
.nav {
  display: flex;
  gap: 4px;
  margin-left: auto;
  overflow-x: auto;
  height: 100%;
}
.nav a {
  position: relative;
  display: inline-flex;
  align-items: center;
  padding: 0 12px;
  height: 100%;
  font-size: var(--text-sm);
  color: var(--content-secondary);
  text-decoration: none;
  white-space: nowrap;
  transition: color var(--fade);
}
.nav a.active {
  color: var(--content);
}
/* Current page: brighter tone plus a jade underline drawn inside the link (nothing for the scroller to clip). */
.nav a.active::after {
  content: "";
  position: absolute;
  left: 12px;
  right: 12px;
  bottom: 0;
  height: 2px;
  background: var(--interactive);
  border-radius: 2px 2px 0 0;
}
.icon-btn {
  background: none;
  border: 0;
  font-size: 18px;
  cursor: pointer;
  color: var(--content-secondary);
  padding: 8px;
  border-radius: var(--radius);
  transition: color var(--fade);
}
@media (hover: hover) and (pointer: fine) {
  .nav a:hover,
  .icon-btn:hover {
    color: var(--content);
  }
}

main {
  max-width: 1280px;
  margin: 0 auto;
  padding: 32px 20px 96px;
}

/* ------------------------------------------------------------------ controls */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  min-height: 38px;
  padding: 0 16px;
  border-radius: var(--radius);
  border: 1px solid var(--border-strong);
  background: transparent;
  color: var(--content);
  font-size: var(--text-sm);
  font-weight: 500;
  line-height: 1.2;
  text-decoration: none;
  cursor: pointer;
  transition:
    background-color var(--fade),
    border-color var(--fade),
    color var(--fade);
}
.btn.primary {
  background: var(--primary);
  color: var(--on-primary);
  border-color: var(--primary);
}
.btn.small {
  min-height: 32px;
  padding: 0 12px;
  font-size: 13px;
}
.btn.danger {
  color: var(--bad);
}
.btn .arrow-end {
  transition: transform 250ms var(--ease-out);
}
@media (hover: hover) and (pointer: fine) {
  .btn:hover {
    border-color: var(--content-secondary);
  }
  .btn.primary:hover {
    background: var(--primary-hover);
    border-color: var(--primary-hover);
  }
  .btn:hover .arrow-end {
    transform: translateX(3px);
  }
}
.btn:active {
  transform: translateY(1px);
}
.linkish {
  background: none;
  border: 0;
  color: var(--content-secondary);
  text-decoration: underline;
  text-underline-offset: 3px;
  cursor: pointer;
  padding: 8px 0;
  font-size: var(--text-sm);
}
select,
input[type="text"],
textarea {
  background: var(--raised);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius);
  padding: 7px 10px;
  max-width: 100%;
  font-size: var(--text-sm);
  transition: border-color var(--fade);
}
select {
  min-height: 38px;
}
textarea,
input[type="text"] {
  width: 100%;
  font-family: var(--mono);
  font-size: 13px;
  letter-spacing: 0;
}
::placeholder {
  color: var(--content-secondary);
}
label {
  display: flex;
  flex-direction: column;
  gap: 6px;
  font-size: 13px;
  color: var(--content-secondary);
}
label.check {
  flex-direction: row;
  align-items: center;
  gap: 8px;
}
label.btn {
  flex-direction: row;
  font-size: var(--text-sm);
  color: var(--content);
}
input[type="checkbox"] {
  accent-color: var(--interactive);
  width: 16px;
  height: 16px;
}
.row {
  display: flex;
  gap: 12px;
  align-items: center;
  flex-wrap: wrap;
}
.row.spread {
  justify-content: space-between;
}
.tools {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 16px 0;
}
.form-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: flex-end;
  margin: 16px 0;
}

/* Two-tone headline: bright statement, muted continuation, same size and weight. */
.two-tone {
  font-weight: 400;
  letter-spacing: -0.02em;
  line-height: 1.12;
  color: var(--content);
}
.two-tone .dim {
  color: var(--content-secondary);
}

/* ------------------------------------------------------------------ learn (home) */
.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(0, 0.9fr);
  gap: 48px;
  align-items: center;
  padding: 24px 0 48px;
}
.hero h1 {
  font-size: var(--text-hero);
  margin: 0 0 28px;
  max-width: 19em;
}
.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}
.band {
  width: 100%;
  max-width: 480px;
  justify-self: end;
  aspect-ratio: 1;
}
.band svg {
  display: block;
  width: 100%;
  height: auto;
}
.band .shape {
  transform-box: fill-box;
  transform-origin: center;
}
@media (prefers-reduced-motion: no-preference) {
  .band.animate .shape {
    animation: shape-in 600ms var(--ease-out) both;
    animation-delay: calc(var(--d) * 28ms);
  }
}
@keyframes shape-in {
  from {
    opacity: 0;
    transform: scale(0.6);
  }
  to {
    opacity: 1;
    transform: none;
  }
}

.stats {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  margin-top: 40px;
  border-top: 1px solid var(--border);
}
.stat {
  padding: 16px 0 0;
}
.stat + .stat {
  padding-left: 20px;
  border-left: 1px solid var(--border);
}
.stat strong {
  display: block;
  font-size: var(--text-display);
  font-weight: 400;
  letter-spacing: -0.03em;
  line-height: 1.05;
  color: var(--content);
  font-variant-numeric: tabular-nums;
}
.stat span {
  color: var(--content-secondary);
  font-size: 13px;
}
.badge {
  display: inline-flex;
  align-items: center;
  min-height: 38px;
  padding: 0 14px;
  border-radius: var(--radius);
  font-size: var(--text-sm);
  background: color-mix(in srgb, var(--good) 10%, transparent);
  border: 1px solid color-mix(in srgb, var(--good) 30%, transparent);
  color: var(--good);
}

.section-title {
  margin: 32px 0 16px;
  font-size: var(--text-lg);
  font-weight: 400;
  letter-spacing: -0.02em;
}
.stages {
  border-bottom: 1px solid var(--border);
}
.stage {
  border-top: 1px solid var(--border);
}
.stage summary {
  display: grid;
  grid-template-columns: 44px minmax(0, 1fr) auto;
  align-items: center;
  gap: 16px;
  padding: 20px 0;
  cursor: pointer;
  list-style: none;
}
.stage summary::-webkit-details-marker {
  display: none;
}
.stage-num {
  font: 400 13px/1 var(--mono);
  color: var(--hue);
  letter-spacing: 0;
}
.stage-title {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 4px 12px;
  min-width: 0;
  font-size: var(--text-lg);
  letter-spacing: -0.02em;
  line-height: 1.2;
}
.stage-title strong {
  font-weight: 400;
  color: var(--content);
}
.stage-title small {
  color: var(--content-secondary);
  font-size: var(--text-sm);
  letter-spacing: -0.01em;
}
.stage-progress {
  display: flex;
  align-items: center;
  gap: 12px;
  font: 400 13px/1 var(--mono);
  color: var(--content-secondary);
  letter-spacing: 0;
}
.meter {
  width: 64px;
  height: 2px;
  background: var(--border-strong);
  border-radius: 2px;
  overflow: hidden;
}
.meter i {
  display: block;
  height: 100%;
  background: var(--hue);
}
.stage-blurb {
  margin: -6px 0 12px 60px;
  color: var(--content-secondary);
  max-width: 60ch;
}
.lessons {
  list-style: none;
  margin: 0;
  padding: 0 0 24px 60px;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 2px 16px;
}
.lessons a {
  display: flex;
  gap: 12px;
  padding: 10px 10px 10px 0;
  border-radius: var(--radius);
  text-decoration: none;
  color: var(--content);
  transition: color var(--fade);
}
.lessons small {
  display: block;
  color: var(--content-secondary);
  font-size: 13px;
  margin-top: 1px;
}
.tick {
  flex: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  border: 1px solid var(--border-strong);
  display: grid;
  place-items: center;
  font-size: 11px;
  margin-top: 3px;
}
.lessons li.done .tick {
  background: var(--hue);
  border-color: var(--hue);
  color: var(--canvas);
}
@media (hover: hover) and (pointer: fine) {
  .stage summary:hover .stage-title strong {
    color: var(--content-strong);
  }
  .lessons a:hover {
    color: var(--content-strong);
  }
  .lessons a:hover .tick {
    border-color: var(--hue);
  }
}

/* ------------------------------------------------------------------ study layout */
.study {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(320px, 1fr);
  gap: 48px;
  align-items: start;
}
.board-col {
  position: sticky;
  top: 82px;
}
.panel {
  min-width: 0;
  max-width: 62ch;
}
.panel h2 {
  margin: 6px 0 12px;
  font-size: 30px;
}
.crumbs {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 13px;
  color: var(--content-secondary);
}
.crumbs a {
  color: var(--content-secondary);
  text-decoration: none;
}
.crumbs a:hover {
  color: var(--content);
}
.dots {
  display: flex;
  gap: 4px;
  margin: 4px 0 24px;
}
.dots span {
  flex: 0 1 28px;
  height: 2px;
  border-radius: 2px;
  background: var(--border-strong);
}
.dots span.past {
  background: color-mix(
    in srgb,
    var(--hue, var(--interactive)) 50%,
    var(--border-strong)
  );
}
.dots span.on {
  background: var(--hue, var(--interactive));
}
.prose {
  color: var(--content);
}
.prose p {
  margin: 0 0 14px;
}
.prose ul,
.prose ol,
.game-note ul {
  margin: 0 0 14px;
  padding-left: 22px;
}
.prose li {
  margin: 4px 0;
}
.prose li::marker {
  color: var(--content-secondary);
}
.prose h3 {
  font-size: var(--text-body);
  font-weight: 500;
  margin: 20px 0 6px;
}
.prose code,
.feedback code {
  font-family: var(--mono);
  font-size: 0.88em;
  background: var(--raised-2);
  padding: 1px 5px;
  border-radius: var(--radius);
  letter-spacing: 0;
}
.feedback {
  border-radius: var(--radius);
  padding: 0;
  margin: 12px 0;
  font-size: 15px;
}
.feedback:not(:empty) {
  padding: 12px 14px;
  background: var(--raised);
  border: 1px solid var(--border-strong);
}
.feedback p {
  margin: 0;
}
.feedback p + p {
  margin-top: 8px;
}
/* Tints, not fills: hue at 10% with a 30% hairline. */
.feedback.good {
  background: color-mix(in srgb, var(--good) 10%, transparent);
  border-color: color-mix(in srgb, var(--good) 30%, transparent);
  color: var(--good);
}
.feedback.bad {
  background: color-mix(in srgb, var(--bad) 10%, transparent);
  border-color: color-mix(in srgb, var(--bad) 30%, transparent);
  color: var(--bad);
}
.feedback.good strong,
.feedback.bad strong {
  color: inherit;
}
.stepnav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  margin-top: 28px;
  padding-top: 20px;
  border-top: 1px solid var(--border);
}
.stepnav .muted {
  font: 400 13px/1 var(--mono);
  letter-spacing: 0;
}
.game-controls {
  display: flex;
  gap: 6px;
}
.game-note:not(:empty) {
  flex-basis: 100%;
  padding: 2px 0 2px 16px;
  border-left: 2px solid var(--hue, var(--interactive));
  border-radius: 0;
}
.game-note p {
  margin: 0 0 6px;
}
.movelist {
  flex-basis: 100%;
  display: flex;
  flex-wrap: wrap;
  gap: 2px;
  max-height: 220px;
  overflow: auto;
  padding: 8px 0;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  font: 400 13px/1.4 var(--mono);
  letter-spacing: 0;
  font-variant-numeric: tabular-nums;
}
.movelist:empty {
  display: none;
}
.movelist .num {
  color: var(--content-secondary);
  padding: 3px 0 3px 6px;
}
.movelist .mv {
  background: none;
  border: 0;
  padding: 3px 6px;
  border-radius: var(--radius);
  cursor: pointer;
  font: inherit;
  color: var(--content);
  transition: background-color var(--fade);
}
.movelist .mv.cur {
  background: color-mix(in srgb, var(--interactive) 22%, transparent);
  color: var(--content-strong);
}
@media (hover: hover) and (pointer: fine) {
  .movelist .mv:not(.cur):hover {
    background: var(--raised-2);
  }
}
.eval {
  margin: 8px 0;
}
.eval .score {
  font: 400 36px/1.1 var(--mono);
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
}
.eval .pv {
  color: var(--content-secondary);
  font: 400 13px/1.5 var(--mono);
  letter-spacing: 0;
}
details.io {
  margin-top: 24px;
  border-top: 1px solid var(--border);
  padding-top: 12px;
}
details.io summary {
  cursor: pointer;
  color: var(--content-secondary);
  font-size: var(--text-sm);
  margin-bottom: 12px;
}
details.io label {
  margin: 8px 0;
}

/* ------------------------------------------------------------------ board */
/* Squares are sized from the board's own width (container units), so nothing goes stale. */
.board-wrap {
  position: relative;
  width: 100%;
  max-width: 640px;
  margin: 0 auto;
  user-select: none;
  -webkit-user-select: none;
  touch-action: none;
  container-type: inline-size;
  --sq: 12.5cqw;
}
.board {
  display: grid;
  grid-template-columns: repeat(8, minmax(0, 1fr));
  grid-template-rows: repeat(8, minmax(0, 1fr));
  aspect-ratio: 1;
  border-radius: var(--radius);
  overflow: hidden;
}
.sq {
  position: relative;
  display: grid;
  place-items: center;
  cursor: pointer;
  overflow: hidden;
  min-width: 0;
  min-height: 0;
}
.sq.light {
  background: var(--sq-light);
}
.sq.dark {
  background: var(--sq-dark);
}
.sq.last::before,
.sq.selected::before,
.sq.mark::before,
.sq.hint::before,
.sq.check::before,
.sq[class*="flash-"]::before {
  content: "";
  position: absolute;
  inset: 0;
}
.sq.last::before {
  background: var(--hl-last);
}
.sq.selected::before {
  background: var(--hl-select);
}
.sq.mark::before {
  background: var(--hl-mark);
}
.sq.hint::before {
  box-shadow: inset 0 0 0 calc(var(--sq) * 0.06) var(--hl-hint);
}
.sq.check::before {
  background: radial-gradient(
    circle,
    rgba(var(--hl-check), 0.95) 0%,
    rgba(var(--hl-check), 0.5) 45%,
    transparent 75%
  );
}
.sq.flash-good::before {
  background: var(--hl-good);
}
.sq.flash-bad::before {
  background: var(--hl-bad);
}
.sq.target::after {
  content: "";
  position: absolute;
  width: 28%;
  height: 28%;
  border-radius: 50%;
  background: rgba(14, 14, 14, 0.26);
  pointer-events: none;
}
.sq.target.capture::after {
  width: 92%;
  height: 92%;
  background: none;
  border: calc(var(--sq) * 0.07) solid rgba(14, 14, 14, 0.26);
  box-sizing: border-box;
}
.piece {
  position: relative;
  z-index: 1;
  font-family:
    "Apple Symbols", "Segoe UI Symbol", "DejaVu Sans", "Noto Sans Symbols 2",
    "Arial Unicode MS", serif;
  font-size: calc(var(--sq) * 0.82);
  line-height: 1;
  pointer-events: none;
  letter-spacing: 0;
}
.piece.white {
  color: #fbf8f2;
  -webkit-text-stroke: calc(var(--sq) * 0.022) #24211d;
  paint-order: stroke fill;
}
.piece.black {
  color: #161412;
  -webkit-text-stroke: calc(var(--sq) * 0.01) #161412;
}
.piece.ghost {
  position: fixed;
  z-index: 100;
  display: grid;
  place-items: center;
  pointer-events: none;
  transform: scale(1.08);
}
.coord {
  position: absolute;
  font: 500 max(10px, calc(var(--sq) * 0.16))/1 var(--mono);
  pointer-events: none;
  letter-spacing: 0;
}
.coord.rank {
  top: 4px;
  left: 4px;
}
.coord.file {
  bottom: 3px;
  right: 5px;
}
.sq.light .coord {
  color: var(--coord-on-light);
}
.sq.dark .coord {
  color: var(--coord-on-dark);
}
.arrows {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
}
.arrow {
  stroke-width: 0.17;
  stroke-linecap: round;
  opacity: 0.85;
}
.arrow.green {
  stroke: #4e9a6b;
}
.head.green {
  fill: #4e9a6b;
}
.arrow.red {
  stroke: #c9696b;
}
.head.red {
  fill: #c9696b;
}
.arrow.blue {
  stroke: #4b8fc9;
}
.head.blue {
  fill: #4b8fc9;
}
.promo {
  position: absolute;
  inset: 0;
  z-index: 5;
  background: rgba(14, 14, 14, 0.62);
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: var(--radius);
}
.promo button {
  width: var(--sq);
  height: var(--sq);
  border-radius: var(--radius);
  border: 1px solid var(--border-strong);
  background: var(--sq-light);
  cursor: pointer;
  font-size: calc(var(--sq) * 0.8);
  line-height: 1;
  padding: 0;
  pointer-events: auto;
  transition: background-color var(--fade);
}
@media (hover: hover) and (pointer: fine) {
  .promo button:hover {
    background: #e8e2d2;
  }
}

/* ------------------------------------------------------------------ dialogs */
.modal-back {
  position: fixed;
  inset: 0;
  z-index: 50;
  background: rgba(14, 14, 14, 0.7);
  display: grid;
  place-items: center;
  padding: 16px;
}
@media (prefers-color-scheme: light) {
  .modal-back {
    background: rgba(14, 14, 14, 0.35);
  }
}
.modal {
  background: var(--raised);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-panel);
  padding: 28px;
  width: min(520px, 100%);
  max-height: 90vh;
  overflow: auto;
}
@media (prefers-reduced-motion: no-preference) {
  .modal {
    animation: modal-in 300ms var(--ease-out) both;
  }
}
@keyframes modal-in {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: none;
  }
}
.modal:focus {
  outline: none;
}
.modal h2 {
  margin: 0 0 8px;
  font-size: 26px;
}
.modal-actions {
  display: flex;
  justify-content: flex-end;
  margin-top: 24px;
  padding-top: 16px;
  border-top: 1px solid var(--border-strong);
}
.choices {
  display: grid;
  margin: 20px 0 8px;
  border-top: 1px solid var(--border-strong);
}
.choice {
  text-align: left;
  padding: 14px 4px;
  border: 0;
  border-bottom: 1px solid var(--border-strong);
  background: none;
  cursor: pointer;
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 2px 12px;
  transition: color var(--fade);
}
.choice strong {
  font-weight: 400;
  color: var(--content);
  font-size: var(--text-body);
}
.choice span {
  grid-column: 1;
  color: var(--content-secondary);
  font-size: var(--text-sm);
}
.choice::after {
  content: "→";
  grid-column: 2;
  grid-row: 1 / span 2;
  color: var(--content-tertiary);
  transition:
    transform 250ms var(--ease-out),
    color var(--fade);
}
@media (hover: hover) and (pointer: fine) {
  .choice:hover strong {
    color: var(--content-strong);
  }
  .choice:hover::after {
    color: var(--interactive);
    transform: translateX(3px);
  }
}

/* ------------------------------------------------------------------ responsive */
@media (max-width: 960px) {
  .hero {
    grid-template-columns: 1fr;
    gap: 32px;
  }
  .band {
    justify-self: stretch;
    max-width: none;
    aspect-ratio: 8 / 3;
    overflow: hidden;
  }
}
@media (max-width: 860px) {
  .study {
    grid-template-columns: 1fr;
    gap: 20px;
  }
  .board-col {
    position: static;
  }
  .panel {
    max-width: none;
  }
  .stage-blurb {
    margin-left: 0;
  }
  .lessons {
    padding-left: 0;
    grid-template-columns: 1fr;
  }
}
@media (max-width: 560px) {
  main {
    padding: 20px 16px 64px;
  }
  .top {
    padding: 0 12px;
    gap: 8px;
  }
  .brand {
    font-size: 0;
    gap: 0;
  }
  .brand .logo {
    font-size: 22px;
  }
  .nav a {
    padding: 0 9px;
  }
  .nav a.active::after {
    left: 9px;
    right: 9px;
  }
  /* One full-width primary action, the two secondary ones side by side. */
  .hero-actions {
    display: grid;
    grid-template-columns: 1fr 1fr;
  }
  .hero-actions > :first-child {
    grid-column: 1 / -1;
  }
  .stat + .stat {
    padding-left: 12px;
  }
  .stat span {
    font-size: 12px;
    white-space: nowrap;
  }
  .stage summary {
    grid-template-columns: 32px minmax(0, 1fr) auto;
    gap: 12px;
  }
  .meter {
    display: none;
  }
  .panel h2 {
    font-size: 26px;
  }
}
@media (max-width: 360px) {
  .wide-only {
    display: none;
  }
  .nav {
    gap: 0;
  }
  .nav a {
    padding: 0 6px;
  }
  .nav a.active::after {
    left: 6px;
    right: 6px;
  }
}
/* Touch screens: at least 40px tap targets. Desktop keeps the compact sizes. */
@media (pointer: coarse) {
  .btn,
  .btn.small,
  select,
  .icon-btn {
    min-height: 40px;
  }
  .movelist .mv {
    min-height: 40px;
    padding: 4px 10px;
  }
  .movelist .num {
    align-self: center;
  }
  details.io summary {
    min-height: 40px;
    display: flex;
    align-items: center;
  }
}