/* BRT site styles: system fonts, one accent colour, light/dark via prefers-color-scheme. */
:root {
  --bg: #fbfbfa;
  --surface: #ffffff;
  --surface-2: #f2f4f5;
  --text: #1c2226;
  --muted: #5b666e;
  --border: #dde2e5;
  --accent: #0e7c86;
  --accent-strong: #0a5f67;
  --accent-soft: #e2f3f4;
  --code-bg: #f2f4f5;
  --viewer-bg: #e6ecf0;
  --error: #a3261b;
  --radius: 12px;
  --shadow: 0 1px 2px rgb(16 24 32 / 6%), 0 4px 16px rgb(16 24 32 / 6%);
  --max: 68rem;
  color-scheme: light;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #111518;
    --surface: #171c20;
    --surface-2: #1e252a;
    --text: #e6eaec;
    --muted: #9aa6ad;
    --border: #2b343a;
    --accent: #4cc3cc;
    --accent-strong: #7fd8de;
    --accent-soft: #15343a;
    --code-bg: #1b2227;
    --viewer-bg: #1a2126;
    --error: #ff8a7a;
    --shadow: 0 1px 2px rgb(0 0 0 / 30%), 0 4px 16px rgb(0 0 0 / 25%);
    color-scheme: dark;
  }
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 400 1rem/1.6 system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
}

img {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--accent-strong);
  text-underline-offset: 0.18em;
}

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

:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 2px;
  border-radius: 4px;
}

.skip-link {
  position: absolute;
  left: 1rem;
  top: -3rem;
  padding: 0.5rem 0.75rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  z-index: 10;
}

.skip-link:focus {
  top: 1rem;
}

.container {
  width: min(100% - 2rem, var(--max));
  margin-inline: auto;
}

/* ------------------------------------------------------------------ header */

.site-header {
  position: sticky;
  top: 0;
  z-index: 5;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: saturate(1.4) blur(10px);
  border-bottom: 1px solid var(--border);
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  min-height: 3.5rem;
}

.brand {
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--text);
  text-decoration: none;
}

.brand span {
  color: var(--muted);
  font-weight: 500;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem 1.1rem;
  font-size: 0.95rem;
}

.site-nav a {
  color: var(--muted);
  text-decoration: none;
}

.site-nav a:hover,
.site-nav a[aria-current="page"] {
  color: var(--text);
}

@media (max-width: 40rem) {
  .brand span {
    display: none;
  }
}

/* ------------------------------------------------------------------ sections */

main {
  padding-bottom: 4rem;
}

section {
  padding-top: 3.5rem;
}

h1,
h2,
h3 {
  line-height: 1.2;
  letter-spacing: -0.01em;
}

h1 {
  font-size: clamp(1.9rem, 4vw, 2.75rem);
  margin: 0 0 0.75rem;
}

h2 {
  font-size: 1.6rem;
  margin: 0 0 1rem;
}

h3 {
  font-size: 1.15rem;
  margin: 0 0 0.5rem;
}

.lead {
  font-size: 1.15rem;
  color: var(--muted);
  max-width: 46rem;
}

.hero {
  padding-top: 2.5rem;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 1.5rem;
}

.button {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.6rem 1.1rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  font-weight: 600;
  text-decoration: none;
}

.button:hover {
  border-color: var(--accent);
  color: var(--text);
}

.button.primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

@media (prefers-color-scheme: dark) {
  .button.primary {
    color: #0b1416;
  }
}

.button.primary:hover {
  background: var(--accent-strong);
  border-color: var(--accent-strong);
}

.grid {
  display: grid;
  gap: 1.25rem;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 19rem), 1fr));
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.4rem 1.5rem;
  box-shadow: var(--shadow);
}

.card p:last-child,
.card ul:last-child {
  margin-bottom: 0;
}

.card .eyebrow {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent-strong);
  margin-bottom: 0.4rem;
}

.env-card {
  display: flex;
  flex-direction: column;
}

.env-card .tasks {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  padding: 0;
  margin: 0.25rem 0 1.25rem;
  list-style: none;
}

.env-card .tasks li {
  font: 500 0.82rem/1.4 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  background: var(--accent-soft);
  color: var(--accent-strong);
  padding: 0.2rem 0.55rem;
  border-radius: 6px;
}

.env-card .button-row {
  margin-top: auto;
}

/* ------------------------------------------------------------------ code */

code,
pre {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  font-size: 0.9rem;
}

:not(pre) > code {
  overflow-wrap: anywhere;
  background: var(--code-bg);
  padding: 0.1rem 0.35rem;
  border-radius: 5px;
}

pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.15rem;
  overflow-x: auto;
  line-height: 1.55;
  margin: 0 0 1.25rem;
}

.code-label {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--muted);
  margin: 0 0 0.4rem;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.25rem;
  font-size: 0.95rem;
}

.table-wrap {
  overflow-x: auto;
}

.table-wrap table {
  min-width: 34rem;
}

th,
td {
  text-align: left;
  padding: 0.6rem 0.75rem;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

th {
  color: var(--muted);
  font-weight: 600;
}

/* ------------------------------------------------------------------ viewer */

.viewer {
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--viewer-bg);
  box-shadow: var(--shadow);
}

.viewer-stage {
  position: relative;
  aspect-ratio: 16 / 9;
  min-height: 16rem;
  max-height: 62vh;
  width: 100%;
}

.viewer-stage canvas {
  display: block;
  width: 100%;
  height: 100%;
  touch-action: none;
  cursor: grab;
}

.viewer-stage canvas:active {
  cursor: grabbing;
}

.viewer-status {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  padding: 1.5rem;
  text-align: center;
  color: var(--muted);
}

.viewer-status[hidden] {
  display: none;
}

.viewer-status.is-error {
  color: var(--error);
}

.viewer-toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  padding: 0.6rem 0.75rem;
  border-top: 1px solid var(--border);
  background: var(--surface);
}

.viewer-toolbar button {
  font: inherit;
  font-size: 0.9rem;
  font-weight: 600;
  padding: 0.35rem 0.9rem;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  cursor: pointer;
}

.viewer-toolbar button:hover:not(:disabled) {
  border-color: var(--accent);
}

.viewer-toolbar button:disabled {
  opacity: 0.5;
  cursor: default;
}

.viewer-readout {
  margin-left: auto;
  font: 500 0.85rem/1 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

.viewer-hint {
  font-size: 0.88rem;
  color: var(--muted);
  margin-top: 0.6rem;
}

/* Open-loop control panel under a viewer (seahorse and swimmer demos). */
.muscle-controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(14rem, 1fr));
  gap: 0.75rem 1.5rem;
  align-items: center;
  margin-top: 0.75rem;
  padding: 0.9rem 1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
}

.muscle-control {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 0.15rem 0.75rem;
  font-size: 0.92rem;
}

.muscle-control input {
  grid-column: 1 / -1;
  width: 100%;
  accent-color: var(--accent);
}

.muscle-control output {
  grid-row: 1;
  grid-column: 2;
  color: var(--muted);
  font: 500 0.85rem/1.6 ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-variant-numeric: tabular-nums;
}

.muscle-toggle {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.92rem;
}

.muscle-toggle input {
  accent-color: var(--accent);
  width: 1.05rem;
  height: 1.05rem;
}

/* ------------------------------------------------------------------ footer */

.site-footer {
  border-top: 1px solid var(--border);
  padding: 2rem 0 3rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.site-footer .container {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 1rem;
}