/* Keel Linux project site. Plain CSS, system fonts, no build step. */

:root {
  color-scheme: light dark;

  --navy: #0B1F3A;
  --teal: #16A6A0;
  --offwhite: #F4F7FA;

  --bg: var(--offwhite);
  --fg: var(--navy);
  --muted: #3F5470;
  --accent: var(--teal);
  --accent-text: #0C6F6B;
  --surface: #FFFFFF;
  --line: #D3DCE6;
  --plate: var(--offwhite);
  --btn-bg: var(--navy);
  --btn-fg: var(--offwhite);
  --code-bg: #E7EDF4;
  --focus: #0C6F6B;

  --gutter: 16px;
  --measure: 62ch;
  --radius: 0.75rem;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: var(--navy);
    --fg: var(--offwhite);
    --muted: #B5C2D2;
    --accent: var(--teal);
    --accent-text: #2FBDB7;
    --surface: #112A4C;
    --line: #28466B;
    --plate: var(--offwhite);
    --btn-bg: var(--teal);
    --btn-fg: var(--navy);
    --code-bg: #163559;
    --focus: var(--teal);
  }
}

:root[data-theme="dark"] {
  --bg: var(--navy);
  --fg: var(--offwhite);
  --muted: #B5C2D2;
  --accent: var(--teal);
  --accent-text: #2FBDB7;
  --surface: #112A4C;
  --line: #28466B;
  --plate: var(--offwhite);
  --btn-bg: var(--teal);
  --btn-fg: var(--navy);
  --code-bg: #163559;
  --focus: var(--teal);
}

/* Base */

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

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

@media (prefers-reduced-motion: no-preference) {
  html {
    scroll-behavior: smooth;
  }
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, "Noto Sans", "Liberation Sans", sans-serif;
  font-size: 1rem;
  line-height: 1.6;
  overflow-x: hidden;
}

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

a {
  color: var(--accent-text);
  text-underline-offset: 0.15em;
}

a:hover {
  text-decoration-thickness: 2px;
}

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

code {
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas,
    "Liberation Mono", "DejaVu Sans Mono", monospace;
  font-size: 0.92em;
  background: var(--code-bg);
  padding: 0.1em 0.4em;
  border-radius: 0.3em;
}

h1,
h2,
h3 {
  line-height: 1.2;
  letter-spacing: -0.01em;
  margin: 0;
}

p {
  margin: 0;
}

p + p {
  margin-top: 1em;
}

.wrap {
  max-width: 72rem;
  margin-inline: auto;
  padding-inline: var(--gutter);
}

@media (min-width: 48rem) {
  .wrap {
    padding-inline: 2rem;
  }
}

.skip {
  position: absolute;
  left: var(--gutter);
  top: -100%;
  padding: 0.5rem 1rem;
  background: var(--surface);
  color: var(--fg);
  border: 1px solid var(--line);
  border-radius: 0.5rem;
  z-index: 10;
}

.skip:focus {
  top: 0.75rem;
}

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

/* Header */

.site-header {
  border-bottom: 1px solid var(--line);
}

.site-header .wrap {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.75rem 1.5rem;
  min-height: 4rem;
  padding-block: 0.75rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  color: var(--fg);
  text-decoration: none;
  font-weight: 700;
  font-size: 1.05rem;
  margin-right: auto;
}

.brand img {
  width: 2rem;
  height: 2rem;
  background: var(--plate);
  border-radius: 0.4rem;
}

.site-nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.25rem 1.25rem;
}

.site-nav a {
  color: var(--fg);
  text-decoration: none;
  font-size: 0.95rem;
}

.site-nav a:hover {
  text-decoration: underline;
  text-decoration-color: var(--accent);
  text-decoration-thickness: 2px;
}

.theme-toggle {
  appearance: none;
  border: 1px solid var(--line);
  background: transparent;
  color: var(--fg);
  width: 2.25rem;
  height: 2.25rem;
  border-radius: 50%;
  display: inline-grid;
  place-items: center;
  cursor: pointer;
  padding: 0;
}

.theme-toggle:hover {
  border-color: var(--accent);
}

.theme-toggle svg {
  width: 1.1rem;
  height: 1.1rem;
}

/* Buttons */

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-top: 2rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.7rem 1.25rem;
  border-radius: 0.5rem;
  border: 1.5px solid var(--btn-bg);
  font-weight: 600;
  text-decoration: none;
  line-height: 1.2;
}

.btn-primary {
  background: var(--btn-bg);
  color: var(--btn-fg);
}

.btn-primary:hover {
  opacity: 0.92;
}

.btn-secondary {
  background: transparent;
  color: var(--fg);
  border-color: var(--fg);
}

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

/* Sections */

section {
  padding-block: 4rem;
  border-top: 1px solid var(--line);
}

@media (min-width: 48rem) {
  section {
    padding-block: 5.5rem;
  }
}

.eyebrow {
  display: block;
  color: var(--accent-text);
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-bottom: 0.75rem;
}

h2 {
  font-size: clamp(1.6rem, 1.2rem + 1.8vw, 2.25rem);
}

.lead {
  color: var(--muted);
  font-size: 1.1rem;
  max-width: var(--measure);
  margin-top: 1rem;
}

/* Hero */

.hero {
  border-top: 0;
  padding-block: 4rem 4.5rem;
}

@media (min-width: 48rem) {
  .hero {
    padding-block: 6rem 7rem;
  }
}

.hero .wrap {
  display: grid;
  gap: 2rem;
  align-items: center;
}

@media (min-width: 40rem) {
  .hero .wrap {
    grid-template-columns: auto 1fr;
    gap: 3rem;
  }
}

.plate {
  width: 8.5rem;
  aspect-ratio: 1;
  border-radius: 1.5rem;
  background: var(--plate);
  border: 1px solid var(--line);
  display: grid;
  place-items: center;
  padding: 0.5rem;
}

@media (min-width: 48rem) {
  .plate {
    width: 11rem;
  }
}

.hero h1 {
  font-size: clamp(2.4rem, 1.6rem + 4vw, 4rem);
  letter-spacing: -0.02em;
}

.hero .tagline {
  font-size: clamp(1.15rem, 1rem + 0.8vw, 1.45rem);
  margin-top: 1rem;
  max-width: 34ch;
  text-wrap: balance;
}

.hero .sub {
  color: var(--muted);
  margin-top: 0.75rem;
  max-width: var(--measure);
}

/* What changes */

.grid-4 {
  list-style: none;
  margin: 2.5rem 0 0;
  padding: 0;
  display: grid;
  gap: 1.25rem;
  grid-template-columns: repeat(auto-fit, minmax(15rem, 1fr));
}

.card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.5rem;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.card .index {
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas,
    "Liberation Mono", monospace;
  font-size: 0.8rem;
  color: var(--accent-text);
  letter-spacing: 0.08em;
}

.card h3 {
  font-size: 1.15rem;
}

.card p {
  color: var(--muted);
  font-size: 0.97rem;
}

/* How it is built */

.build {
  display: grid;
  gap: 2.5rem;
  margin-top: 2.5rem;
  align-items: start;
}

@media (min-width: 56rem) {
  .build {
    grid-template-columns: minmax(0, 3fr) minmax(0, 2fr);
    gap: 3.5rem;
  }
}

.diagram {
  margin: 0;
}

.diagram svg {
  width: 100%;
  max-width: 36rem;
  height: auto;
  font-size: 15px;
}

.diagram .mono {
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas,
    "Liberation Mono", monospace;
  font-size: 12.5px;
}

.diagram .label {
  font-weight: 700;
}

.diagram .note {
  font-size: 12px;
  opacity: 0.75;
}

.diagram figcaption {
  color: var(--muted);
  font-size: 0.95rem;
  max-width: var(--measure);
  margin-top: 1.25rem;
}

.measured h3 {
  font-size: 1.1rem;
}

.measured .hint {
  color: var(--muted);
  font-size: 0.92rem;
  margin-top: 0.35rem;
}

.measured dl {
  margin: 1.25rem 0 0;
  border-top: 1px solid var(--line);
}

.measured .row {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 1rem;
  padding: 0.85rem 0;
  border-bottom: 1px solid var(--line);
}

.measured dt {
  color: var(--muted);
  font-size: 0.95rem;
}

.measured dd {
  margin: 0;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  white-space: nowrap;
}

.measured dd small {
  font-weight: 400;
  color: var(--muted);
  font-size: 0.85em;
}

/* Standards */

.standards {
  list-style: none;
  margin: 2.5rem 0 0;
  padding: 0;
  display: grid;
  gap: 1.5rem 2.5rem;
}

@media (min-width: 48rem) {
  .standards {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

.standards li {
  position: relative;
  padding-left: 1.5rem;
}

.standards li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.55rem;
  width: 0.7rem;
  height: 0.7rem;
  background: var(--accent);
  border-radius: 2px;
}

.standards strong {
  display: block;
  font-size: 1.05rem;
}

.standards p {
  color: var(--muted);
  font-size: 0.97rem;
  margin-top: 0.25rem;
}

/* Status */

.status .text {
  max-width: var(--measure);
  margin-top: 1.5rem;
}

.status h3 {
  font-size: 1.1rem;
  margin-top: 2.5rem;
}

.next {
  margin: 1rem 0 0;
  padding-left: 1.4rem;
  max-width: var(--measure);
  display: grid;
  gap: 0.6rem;
}

.next li::marker {
  color: var(--accent-text);
  font-weight: 700;
}

/* Footer */

.site-footer {
  border-top: 1px solid var(--line);
  padding-block: 2.5rem;
  color: var(--muted);
  font-size: 0.92rem;
}

.site-footer .wrap {
  display: grid;
  gap: 1rem;
}

.site-footer p {
  max-width: var(--measure);
}

/* Secondary pages */

.page {
  border-top: 0;
  padding-block: 3.5rem 4.5rem;
}

.page h1 {
  font-size: clamp(1.9rem, 1.3rem + 2.4vw, 2.75rem);
  letter-spacing: -0.02em;
}

.guide {
  max-width: var(--measure);
  margin-top: 2.5rem;
  display: grid;
  gap: 1.75rem;
}

.guide h2 {
  font-size: 1.1rem;
  margin-bottom: 0.4rem;
}

.guide ul {
  margin: 0;
  padding-left: 1.25rem;
  display: grid;
  gap: 0.35rem;
}

.guide li::marker {
  color: var(--accent);
}