:root {
  color-scheme: light;

  /* Approved palette sampled from the UHD mockups. */
  --color-white: #ffffff;
  --color-canvas: #eef1f5;
  --color-surface: #f8f9fb;
  --color-surface-subtle: #e9edf3;
  --color-navy-950: #00122e;
  --color-navy-900: #051630;
  --color-navy-850: #051c3c;
  --color-navy-800: #071a3a;
  --color-navy-700: #10284c;
  --color-indigo-900: #17105c;
  --color-indigo-700: #25256b;
  --color-text: #111827;
  --color-text-soft: #3f495a;
  --color-text-muted: #6b7280;
  --color-border: #d7dde7;
  --color-border-strong: #bdc7d5;
  --color-orange-500: #ff6500;
  --color-orange-400: #ff841a;
  --color-orange-100: #fff1e7;
  --color-blue-500: #287aea;
  --color-blue-100: #eaf3ff;
  --color-violet-500: #6552f9;
  --color-violet-100: #f0edff;
  --color-green-500: #30b886;
  --color-green-100: #e7f8f1;
  --color-yellow-500: #f4b223;
  --color-yellow-100: #fff8df;
  --color-red-500: #ef5261;
  --color-red-100: #fff0f2;

  /* Semantic aliases. */
  --color-background: var(--color-canvas);
  --color-primary: var(--color-orange-500);
  --color-primary-hover: #e85c00;
  --color-primary-dark: #d85300;
  --color-accent: var(--color-green-500);
  --color-focus: #79a9ff;
  --color-link: #155bd7;

  --gradient-hero: linear-gradient(110deg, var(--color-navy-850) 0%, #071e43 54%, var(--color-indigo-900) 100%);
  --gradient-hero-panel: linear-gradient(120deg, rgb(49 65 129 / 88%), rgb(37 24 116 / 92%));
  --gradient-primary: linear-gradient(135deg, var(--color-orange-500), var(--color-orange-400));
  --gradient-number: linear-gradient(135deg, var(--color-blue-500), var(--color-violet-500));
  --gradient-cta: linear-gradient(105deg, #f7f1ff, #fff5ea);

  /* Typography. Poppins is the closest named family in the supplied raster spec. */
  --font-sans: "Poppins", "Segoe UI", Arial, sans-serif;
  --font-mono: "Cascadia Code", "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  --font-size-2xs: 0.6875rem;
  --font-size-xs: 0.75rem;
  --font-size-sm: 0.8125rem;
  --font-size-md: 0.875rem;
  --font-size-base: 1rem;
  --font-size-lg: 1.125rem;
  --font-size-xl: 1.25rem;
  --font-size-2xl: 1.5rem;
  --font-size-3xl: 2rem;
  --font-size-4xl: 2.5rem;
  --font-size-5xl: clamp(2.5rem, 4.4vw, 3.5rem);
  --font-weight-regular: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-weight-bold: 700;
  --font-weight-extrabold: 800;
  --line-height-tight: 1.15;
  --line-height-heading: 1.25;
  --line-height-body: 1.65;

  /* Layout and rhythm. */
  --container-width: 84rem;
  --container-narrow: 70rem;
  --article-width: 48rem;
  --course-sidebar-width: 17.5rem;
  --utility-rail-width: 15rem;
  --page-gutter: clamp(1rem, 3.35vw, 3rem);
  --section-space: clamp(4rem, 7vw, 6rem);
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 2.5rem;
  --space-8: 3rem;
  --space-9: 4rem;
  --space-10: 5rem;
  --space-11: 6rem;

  --border-thin: 0.0625rem;
  --radius-xs: 0.375rem;
  --radius-small: 0.5rem;
  --radius-medium: 0.75rem;
  --radius-large: 1rem;
  --radius-xl: 1.25rem;
  --radius-pill: 999rem;
  --shadow-card: 0 0.5rem 1.5rem rgb(0 18 46 / 7%);
  --shadow-raised: 0 1rem 2.5rem rgb(0 18 46 / 12%);
  --shadow-button: 0 0.5rem 1.25rem rgb(255 101 0 / 25%);
  --transition-fast: 160ms ease;
  --transition-base: 220ms ease;
  --z-header: 50;
  --z-menu: 60;
}

html[data-theme="dark"] {
  color-scheme: dark;
  --color-canvas: #06162f;
  --color-surface: #0b203f;
  --color-surface-subtle: #10284c;
  --color-text: #f4f7fb;
  --color-text-soft: #cad4e2;
  --color-text-muted: #9eacc0;
  --color-border: #253c5f;
  --color-border-strong: #3a557d;
  --color-background: #06162f;
  --color-link: #8fbaff;
  --color-focus: #ffad70;
  --gradient-cta: linear-gradient(105deg, #14254b, #25203d);
  --shadow-card: 0 0.5rem 1.5rem rgb(0 0 0 / 24%);
  --shadow-raised: 0 1rem 2.5rem rgb(0 0 0 / 34%);
}

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

html {
  min-width: 20rem;
  scroll-behavior: smooth;
  scroll-padding-top: 6rem;
}

body {
  min-height: 100vh;
  margin: 0;
  display: grid;
  grid-template-rows: auto 1fr auto;
  background: var(--color-background);
  color: var(--color-text);
  font-family: var(--font-sans);
  font-size: var(--font-size-base);
  font-weight: var(--font-weight-regular);
  line-height: var(--line-height-body);
  text-rendering: optimizeLegibility;
}

img,
picture,
svg,
video,
canvas {
  max-width: 100%;
  display: block;
}

button,
input,
select,
textarea {
  font: inherit;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

a {
  color: var(--color-link);
  text-underline-offset: 0.2em;
  text-decoration-thickness: 0.08em;
}

a:hover {
  color: #0c47b2;
}

:focus-visible {
  outline: 0.1875rem solid var(--color-focus);
  outline-offset: 0.1875rem;
}

h1,
h2,
h3,
h4,
p,
ul,
ol,
dl,
blockquote,
pre,
figure {
  margin-top: 0;
}

h1,
h2,
h3,
h4 {
  color: var(--color-text);
  font-weight: var(--font-weight-bold);
  line-height: var(--line-height-heading);
  text-wrap: balance;
}

h1 {
  margin-bottom: var(--space-5);
  font-size: var(--font-size-5xl);
  letter-spacing: -0.035em;
}

h2 {
  margin-bottom: var(--space-4);
  font-size: clamp(1.625rem, 2.8vw, var(--font-size-3xl));
  letter-spacing: -0.02em;
}

h3 {
  margin-bottom: var(--space-3);
  font-size: var(--font-size-xl);
}

h4 {
  margin-bottom: var(--space-2);
  font-size: var(--font-size-base);
}

small {
  font-size: var(--font-size-sm);
}

code,
kbd,
samp,
pre {
  font-family: var(--font-mono);
}

::selection {
  background: rgb(101 82 249 / 22%);
}

.container {
  width: min(calc(100% - (2 * var(--page-gutter))), var(--container-width));
  margin-inline: auto;
}

.container--narrow {
  max-width: var(--container-narrow);
}

.site-main {
  width: 100%;
}

.section {
  padding-block: var(--section-space);
}

.section--compact {
  padding-block: clamp(2.5rem, 5vw, 4rem);
}

.section--surface {
  background: var(--color-surface);
}

.section--muted {
  background: var(--color-canvas);
}

.section--dark {
  background: var(--color-navy-800);
  color: #cbd5e1;
}

.section--dark :is(h1, h2, h3, h4) {
  color: var(--color-white);
}

.stack {
  display: flex;
  flex-direction: column;
  gap: var(--stack-space, var(--space-5));
}

.cluster {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--cluster-space, var(--space-3));
}

.grid {
  display: grid;
  grid-template-columns: repeat(var(--grid-columns, 3), minmax(0, 1fr));
  gap: var(--grid-gap, var(--space-5));
}

.grid--2 { --grid-columns: 2; }
.grid--3 { --grid-columns: 3; }
.grid--4 { --grid-columns: 4; }
.grid--5 { --grid-columns: 5; }

.split-layout {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(18rem, 0.65fr);
  gap: var(--space-6);
  align-items: start;
}

.article-layout {
  display: grid;
  grid-template-columns: var(--course-sidebar-width) minmax(0, var(--article-width)) var(--utility-rail-width);
  justify-content: center;
  align-items: start;
  gap: var(--space-6);
}

.architecture-shell {
  padding-block: var(--space-9);
}

.error-shell {
  display: grid;
  align-items: center;
  padding-block: var(--space-8);
}

.eyebrow {
  width: fit-content;
  margin-bottom: var(--space-3);
  padding: 0.35rem 0.7rem;
  border: var(--border-thin) solid rgb(255 101 0 / 42%);
  border-radius: var(--radius-pill);
  color: var(--color-orange-500);
  font-size: var(--font-size-xs);
  font-weight: var(--font-weight-semibold);
  letter-spacing: 0.02em;
}

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

.text-accent {
  color: var(--color-orange-500);
}

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

.noscript-message {
  position: fixed;
  right: var(--space-4);
  bottom: var(--space-4);
  left: var(--space-4);
  z-index: 100;
  margin: 0;
  padding: var(--space-3) var(--space-4);
  border: var(--border-thin) solid var(--color-border);
  border-radius: var(--radius-small);
  background: var(--color-surface);
  box-shadow: var(--shadow-raised);
  text-align: center;
}
/* Folder/URL/SEO rulebook: visible breadcrumbs without changing approved hero geometry. */
main { position: relative; }
.seo-breadcrumbs--overlay {
  position: absolute;
  z-index: 2;
  top: .65rem;
  left: 50%;
  width: min(calc(100% - 2rem), var(--container-width));
  padding: 0;
  border: 0;
  transform: translateX(-50%);
  display: flex;
  flex-wrap: wrap;
  gap: .45rem;
  background: transparent;
  color: rgb(255 255 255 / 78%);
  font-size: var(--font-size-xs);
  line-height: 1.4;
}
.seo-breadcrumbs--overlay a { color: inherit; }
.seo-breadcrumbs--overlay a:hover { color: var(--color-white); }
html[data-theme] .seo-breadcrumbs--overlay {
  border: 0;
  background: transparent;
  color: rgb(255 255 255 / 78%);
}
@media (max-width: 42rem) { .seo-breadcrumbs--overlay { top: .45rem; font-size: .72rem; } }