:root {
  --color-bg: #ffffff;
  --color-bg-alt: #f4f4f5;
  --color-text: #1a1a1a;
  --color-text-muted: #5a5a5a;
  --color-border: #dddddd;
  --color-accent: #1a5fb4;
  --color-code-bg: #f0f0f2;
  --color-shadow: rgba(20, 20, 25, 0.14);
  --color-mark-bg: #fff2a8;
  --color-mark-text: #1a1a1a;

  /* Colorblind-safe tier colors (Okabe-Ito palette), distinguishable from
     one another regardless of color vision. */
  --tier-beginner: #009e73;
  --tier-intermediate: #b3720a;
  --tier-advanced: #d55e00;

  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica,
    Arial, sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Consolas,
    "Liberation Mono", Menlo, monospace;

  --content-width: 70ch;
  --sidebar-width: 260px;
  --space-1: 0.5rem;
  --space-2: 1rem;
  --space-3: 1.5rem;
  --space-4: 2.5rem;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-bg: #16181c;
    --color-bg-alt: #1e2126;
    --color-text: #e6e6e6;
    --color-text-muted: #a0a0a0;
    --color-border: #33363c;
    --color-accent: #6cb2ff;
    --color-code-bg: #1e2126;

    --tier-beginner: #33cda6;
    --tier-intermediate: #ffb833;
    --tier-advanced: #ff8a4c;

    --color-shadow: rgba(0, 0, 0, 0.45);
    --color-mark-bg: #5a4a12;
    --color-mark-text: #ffe28a;
  }
}

* {
  box-sizing: border-box;
}

html {
  color-scheme: light dark;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  background: var(--color-bg);
  color: var(--color-text);
  line-height: 1.6;
}

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

.layout {
  display: flex;
  align-items: flex-start;
  min-height: 100vh;
}

.sidebar {
  width: var(--sidebar-width);
  flex-shrink: 0;
  padding: var(--space-3) var(--space-2);
  border-right: 1px solid var(--color-border);
  background: var(--color-bg-alt);
  position: sticky;
  top: 0;
  height: 100vh;
  overflow-y: auto;
}

.content {
  flex: 1;
  padding: var(--space-4) var(--space-3);
  min-width: 0;
}

.page {
  max-width: var(--content-width);
  margin: 0 auto;
}

.tier-index .tier-page-list {
  max-width: var(--content-width);
  margin: var(--space-3) auto 0;
  list-style: decimal;
  padding-left: 1.4rem;
}

.tier-page-list li {
  padding: var(--space-2) 0;
  border-top: 1px solid var(--color-border);
}

.tier-page-list li p {
  margin: 0.25rem 0 0;
  color: var(--color-text-muted);
}

.nav-home {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--color-text);
  text-decoration: none;
  margin-bottom: var(--space-2);
}

.nav-logo {
  flex-shrink: 0;
  border-radius: 50%;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.search {
  position: relative;
  margin-bottom: var(--space-3);
}

.search-icon {
  position: absolute;
  top: 50%;
  left: 0.6rem;
  transform: translateY(-50%);
  color: var(--color-text-muted);
  pointer-events: none;
}

.search-input {
  width: 100%;
  font: inherit;
  color: var(--color-text);
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  padding: 0.45rem 2.1rem 0.45rem 2rem;
  transition: border-color 0.15s ease;
}

.search-input::placeholder {
  color: var(--color-text-muted);
}

.search-input:focus {
  outline: none;
  border-color: var(--color-accent);
}

/* Search inputs get a native clear ("x") button - drop it so it doesn't
   collide with the "/" shortcut hint sitting in the same corner. */
.search-input::-webkit-search-cancel-button {
  display: none;
}

.search-kbd {
  position: absolute;
  top: 50%;
  right: 0.5rem;
  transform: translateY(-50%);
  font-family: var(--font-mono);
  font-size: 0.72rem;
  color: var(--color-text-muted);
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: 0.05rem 0.4rem;
  pointer-events: none;
}

.search-input:focus ~ .search-kbd {
  display: none;
}

.search-results {
  position: absolute;
  z-index: 20;
  top: calc(100% + 0.4rem);
  left: 0;
  right: 0;
  max-height: min(60vh, 26rem);
  overflow-y: auto;
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  box-shadow: 0 12px 28px var(--color-shadow);
  padding: 0.35rem;
}

.search-result {
  display: block;
  padding: 0.5rem 0.6rem;
  border-radius: 6px;
  text-decoration: none;
  color: var(--color-text);
}

.search-result + .search-result {
  margin-top: 0.1rem;
}

.search-result:hover,
.search-result.is-active {
  background: var(--color-bg-alt);
}

.search-result-title {
  display: block;
  font-weight: 600;
  font-size: 0.92rem;
}

.search-result-excerpt {
  display: block;
  margin-top: 0.15rem;
  font-size: 0.82rem;
  color: var(--color-text-muted);
  line-height: 1.45;
}

.search-result-excerpt mark {
  background: var(--color-mark-bg);
  color: var(--color-mark-text);
  border-radius: 2px;
  padding: 0 0.1em;
}

.search-empty {
  margin: 0;
  padding: 0.6rem;
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

.nav-tiers {
  list-style: none;
  margin: 0;
  padding: 0;
}

.nav-tier {
  margin-bottom: var(--space-2);
}

.nav-tier > details > summary {
  list-style: none;
  cursor: pointer;
}

.nav-tier > details > summary::-webkit-details-marker {
  display: none;
}

.nav-tier-title {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  font-weight: 600;
  text-decoration: none;
  color: var(--color-text);
  padding: 0.2rem 0;
}

.nav-tier-title.is-current,
.nav-tier-title:hover {
  color: var(--color-accent);
}

.tier-dot {
  display: inline-block;
  width: 0.55rem;
  height: 0.55rem;
  border-radius: 50%;
  flex-shrink: 0;
}

.tier-dot--beginner {
  background: var(--tier-beginner);
}

.tier-dot--intermediate {
  background: var(--tier-intermediate);
}

.tier-dot--advanced {
  background: var(--tier-advanced);
}

.nav-pages {
  list-style: none;
  margin: 0.2rem 0 0;
  padding-left: var(--space-2);
  border-left: 1px solid var(--color-border);
}

.nav-pages li {
  margin: 0.15rem 0;
}

.nav-pages a {
  display: block;
  text-decoration: none;
  color: var(--color-text-muted);
  font-size: 0.92rem;
  padding: 0.1rem 0;
}

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

.nav-footer-links {
  margin-top: var(--space-3);
  padding-top: var(--space-2);
  border-top: 1px solid var(--color-border);
}

.nav-footer-links a {
  display: block;
  padding: 0.1rem 0;
  color: var(--color-text-muted);
  text-decoration: none;
}

.nav-footer-links a:hover {
  color: var(--color-accent);
}

.breadcrumbs {
  max-width: var(--content-width);
  margin: 0 auto var(--space-3);
  font-size: 0.9rem;
  color: var(--color-text-muted);
}

.breadcrumbs a {
  color: var(--color-text-muted);
}

.crumb-sep {
  margin: 0 0.4rem;
}

.crumb-current {
  color: var(--color-text);
}

.tier-badge {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.03em;
  padding: 0.15rem 0.6rem;
  border-radius: 999px;
  margin-bottom: var(--space-1);
}

.tier-badge--beginner {
  color: var(--tier-beginner);
  border: 1px solid var(--tier-beginner);
  background: color-mix(in srgb, var(--tier-beginner) 12%, transparent);
}

.tier-badge--intermediate {
  color: var(--tier-intermediate);
  border: 1px solid var(--tier-intermediate);
  background: color-mix(in srgb, var(--tier-intermediate) 12%, transparent);
}

.tier-badge--advanced {
  color: var(--tier-advanced);
  border: 1px solid var(--tier-advanced);
  background: color-mix(in srgb, var(--tier-advanced) 12%, transparent);
}

.page-header h1 {
  margin: 0.3rem 0;
}

.page-summary {
  font-size: 1.1rem;
  color: var(--color-text-muted);
  margin-top: 0;
}

.page-meta {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  display: flex;
  gap: var(--space-2);
}

.page-tags {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  padding: 0;
  margin: var(--space-1) 0 var(--space-3);
}

.page-tags li {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 999px;
  padding: 0.1rem 0.7rem;
  font-size: 0.78rem;
  color: var(--color-text-muted);
}

.page-prereqs {
  background: var(--color-bg-alt);
  border: 1px solid var(--color-border);
  border-radius: 6px;
  padding: 0.6rem var(--space-2);
  margin: var(--space-2) 0 var(--space-3);
  font-size: 0.92rem;
}

.page-prereqs strong {
  color: var(--color-text-muted);
  font-weight: 600;
}

.page-prereqs ul {
  margin: 0.3rem 0 0;
  padding-left: 1.2rem;
}

.page pre,
.page code {
  font-family: var(--font-mono);
  font-size: 0.9em;
}

.page code {
  background: var(--color-code-bg);
  padding: 0.1em 0.35em;
  border-radius: 4px;
}

.page pre {
  background: var(--color-code-bg);
  padding: var(--space-2);
  border-radius: 6px;
  overflow-x: auto;
  border: 1px solid var(--color-border);
}

.page pre code {
  background: none;
  padding: 0;
}

.page blockquote {
  margin: var(--space-2) 0;
  padding: 0.2rem var(--space-2);
  border-left: 3px solid var(--color-accent);
  color: var(--color-text-muted);
}

.page table {
  border-collapse: collapse;
  width: 100%;
  margin: var(--space-2) 0;
}

.page th,
.page td {
  border: 1px solid var(--color-border);
  padding: 0.4rem 0.6rem;
  text-align: left;
}

.site-footer {
  text-align: center;
  padding: var(--space-3);
  color: var(--color-text-muted);
  font-size: 0.85rem;
  border-top: 1px solid var(--color-border);
}

@media (max-width: 800px) {
  .layout {
    flex-direction: column;
  }

  .sidebar {
    width: 100%;
    height: auto;
    position: static;
    border-right: none;
    border-bottom: 1px solid var(--color-border);
  }

  .content {
    padding: var(--space-3) var(--space-2);
  }
}