/* Shared visual system for STA 235 Fall 2026 interactive lessons. */
:root {
  --ink: #1f2f3d;
  --muted: #647582;
  --paper: #fbfcfb;
  --bg: #fbfcfb;
  --panel: #ffffff;
  --grid: #dbe4e8;
  --line: #dbe4e8;
  --teal: #31776f;
  --blue: #3c78a8;
  --red: #c74d58;
  --purple: #8070a4;
  --gold: #d99a2b;
  --green: #237047;
  --orange: #a84d18;
  --pale: #eef5f5;
  --pale-teal: #eef5f5;
  --pale2: #eef5f5;
  --soft-teal: #eef5f5;
  --soft-blue: #edf3f7;
  --soft-orange: #fff5ed;
  --lav: #f5f2fa;
}

html { color-scheme: light; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 16px/1.55 system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

header {
  background: transparent;
  color: var(--ink);
  padding: 32px 20px 0;
}

header > div,
header div,
main,
.page {
  width: 100%;
  max-width: 1180px;
  margin-right: auto;
  margin-left: auto;
}

main:not(.page) { padding: 0 20px 54px; }
.page { padding: 32px 20px 54px; }
header + main { padding-top: 0; }

h1,
.title {
  max-width: 920px;
  margin: 12px 0 10px;
  color: var(--ink);
  font-size: clamp(2rem, 4.6vw, 3.45rem);
  font-weight: 500;
  letter-spacing: -.045em;
  line-height: 1.04;
}

h2 { color: var(--ink); }

.eyebrow {
  margin: 0;
  color: var(--teal);
  font-size: .74rem;
  font-weight: 800;
  letter-spacing: .14em;
  opacity: 1;
  text-transform: uppercase;
}

header p,
.subtitle,
.intro {
  max-width: 810px;
  margin: 0 0 26px;
  color: var(--muted);
  font-size: 1rem;
  line-height: 1.55;
  opacity: 1;
}

.topline {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.nav { display: flex; gap: 7px; flex-wrap: wrap; }
.nav a {
  border: 1px solid var(--grid);
  border-radius: 7px;
  padding: 6px 9px;
  color: var(--muted);
  font-size: .8rem;
  font-weight: 700;
  text-decoration: none;
}
.nav a:hover,
.nav a[aria-current="page"] {
  border-color: var(--teal);
  background: #f4f9f8;
  color: var(--teal);
}

section { scroll-margin-top: 20px; }

.card,
.model-card,
.term,
.mini,
.step,
.steps > div {
  border: 1px solid var(--grid);
  border-radius: 10px;
  background: var(--panel);
  box-shadow: none;
}

.card { padding: 16px; }

.concept,
.note,
.callout {
  border: 0;
  border-left: 4px solid var(--teal);
  border-radius: 0;
  background: var(--pale);
  color: var(--muted);
  line-height: 1.5;
  padding: 14px 16px;
}

.concept strong,
.note strong,
.callout strong { color: var(--ink); }

.summary,
.reading {
  border-radius: 0;
  border-left: 3px solid var(--purple);
  background: var(--lav);
  color: var(--muted);
}

.summary strong,
.reading strong,
.reading h3 { color: var(--ink); }

button,
.button {
  border: 1px solid var(--grid);
  border-radius: 7px;
  background: #fff;
  color: var(--ink);
  font: inherit;
  font-size: .84rem;
  font-weight: 750;
  padding: 8px 11px;
  cursor: pointer;
}

button:hover,
.button:hover {
  border-color: var(--teal);
  background: #f4f9f8;
  color: var(--teal);
}

button:disabled,
.button:disabled { cursor: not-allowed; opacity: .45; }

button:focus-visible,
.button:focus-visible,
a:focus-visible,
select:focus-visible,
input:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--teal) 32%, transparent);
  outline-offset: 2px;
}

.button.primary {
  border-color: var(--teal);
  background: var(--teal);
  color: #fff;
}
.button.primary:hover { border-color: #28645e; background: #28645e; color: #fff; }

select {
  border: 1px solid #b8c5cc;
  border-radius: 7px;
  background: #fff;
  color: var(--ink);
}
input[type="range"] { accent-color: var(--teal); }

.selection-picker {
  min-width: 0;
  margin: .4rem 0;
  padding: 0;
  border: 0;
}

.selection-picker legend {
  margin-bottom: .45rem;
  padding: 0;
  color: var(--ink);
  font-weight: 700;
}

.selection-options {
  display: flex;
  gap: 7px;
  flex-wrap: wrap;
}

.selection-options label { margin: 0; cursor: pointer; }

.selection-options input {
  position: absolute;
  width: 1px;
  height: 1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
}

.selection-options span {
  display: inline-flex;
  min-height: 38px;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--grid);
  border-radius: 7px;
  background: #fff;
  color: var(--muted);
  font-size: .88rem;
  font-weight: 750;
  padding: 7px 11px;
  transition: background-color .15s ease, border-color .15s ease, color .15s ease;
}

.selection-options label:hover span {
  border-color: var(--teal);
  color: var(--teal);
}

.selection-options input:checked + span {
  border-color: var(--teal);
  background: var(--teal);
  color: #fff;
}

.selection-options input:focus-visible + span {
  outline: 3px solid color-mix(in srgb, var(--teal) 32%, transparent);
  outline-offset: 2px;
}

code,
.equation,
.model {
  border: 1px solid var(--grid);
  border-radius: 6px;
  background: #f7f9f9;
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Consolas, monospace;
}

code { padding: .08rem .28rem; }
.equation,
.model { padding: 9px 10px; }

.chart-frame,
.diagnostic,
.table-wrap {
  border-color: var(--grid);
  border-radius: 9px;
  background: var(--panel);
}

table { background: var(--panel); }
th, td { border-color: var(--grid); }
th { color: var(--muted); }

footer,
.footer {
  border-top: 1px solid var(--grid);
  margin-top: 30px;
  padding-top: 15px;
  color: var(--muted);
  font-size: .8rem;
  line-height: 1.45;
}

@media (max-width: 680px) {
  header { padding: 24px 12px 0; }
  main:not(.page) { padding: 0 12px 40px; }
  .page { padding: 24px 12px 40px; }
  h1, .title { font-size: 2.15rem; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; transition: none !important; }
}