/* ============================================================
   IB Knowledge Hub — Design Tokens (Epic 6: Design System)
   Retokened to Design System v1.1 (Sprint 1.1 — UI Polish)
   ============================================================ */
@import url('https://fonts.googleapis.com/css2?family=Archivo:wght@400;800&display=swap');

:root {
  /* Color palette — v1.1 (gold accent + blue gradient removed) */
  --color-primary: #2d2b2b;      /* Ink — headings, primary text, header */
  --color-secondary: #ae1800;    /* Secondary — links, secondary emphasis */
  --color-accent: #ec3013;       /* Accent — used sparingly: primary CTAs, focus */
  --color-bg: #f3f2f2;           /* Background — paper */
  --color-bg-alt: #eae9e9;       /* Surface */
  --color-border: #d8d5d4;       /* Minimal borders */
  --color-text: #201e1d;
  --color-text-muted: #63605f;
  --color-white: #ffffff;

  /* Typography */
  --font-family: "Archivo", system-ui, sans-serif;
  --font-size-base: 18px;   /* Body — desktop reading comfort */
  --line-height-base: 1.7;  /* long-form article reading */
  --font-size-sm: 15px;     /* UI */
  --font-size-lg: 20px;     /* H4 */
  --font-size-xl: 25px;     /* H3 */
  --font-size-2xl: 32px;    /* H2 */
  --font-size-3xl: 42px;    /* H1 */
  --font-size-xs: 13px;

  /* Spacing scale — 8-point system */
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;

  /* Layout */
  --max-width: 1080px;
  --radius: 4px;
  --radius-pill: 999px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  font-family: var(--font-family);
  font-size: var(--font-size-base);
  line-height: var(--line-height-base);
  color: var(--color-text);
  background: var(--color-bg);
}

h1, h2, h3, h4 {
  font-family: var(--font-family);
  font-weight: 800;
  color: var(--color-primary);
  line-height: 1.2;
  margin-top: 0;
}

h1 { font-size: var(--font-size-3xl); }
h2 { font-size: var(--font-size-2xl); margin-top: var(--space-7); }
h3 { font-size: var(--font-size-xl); margin-top: var(--space-6); }
h4 { font-size: var(--font-size-lg); }

a { color: var(--color-secondary); text-decoration: none; }
a:hover { text-decoration: underline; }

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

.container {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--space-4);
}

/* ---------- Accessibility: skip link ---------- */
.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 1000;
  background: var(--color-primary);
  color: var(--color-white);
  padding: var(--space-2) var(--space-4);
  font-weight: 800;
  border-radius: 0 0 var(--radius) 0;
}
.skip-link:focus {
  left: 0;
}

:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

.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;
}

/* ---------- Header ---------- */
.site-header {
  background: var(--color-primary);
  color: var(--color-white);
  position: sticky;
  top: 0;
  z-index: 100;
}
.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-top: var(--space-4);
  padding-bottom: var(--space-4);
}
.site-header .logo {
  font-size: var(--font-size-lg);
  font-weight: 800;
  color: var(--color-white);
}
.site-header .logo span { color: var(--color-accent); }

/* ---------- Navigation ---------- */
.nav-toggle {
  display: none;
  background: none;
  border: 2px solid var(--color-white);
  color: var(--color-white);
  font-size: 1rem;
  padding: var(--space-1) var(--space-3);
  border-radius: var(--radius);
  cursor: pointer;
}
.main-nav ul {
  list-style: none;
  display: flex;
  gap: var(--space-5);
  margin: 0;
  padding: 0;
}
.main-nav a {
  color: var(--color-white);
  font-weight: 800;
  font-size: var(--font-size-xs);
  letter-spacing: 0.02em;
  text-transform: uppercase;
  padding: var(--space-1) 0;
  border-bottom: 2px solid transparent;
}
.main-nav a:hover { color: var(--color-accent); text-decoration: none; }
.main-nav a[aria-current="page"] {
  color: var(--color-accent);
  border-bottom-color: var(--color-accent);
}

/* ---------- Footer ---------- */
.site-footer {
  background: var(--color-bg-alt);
  border-top: 1px solid var(--color-border);
  margin-top: var(--space-8);
  padding: var(--space-6) 0;
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}
.site-footer .footer-cols {
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--space-5);
}
.site-footer h4 {
  color: var(--color-primary);
  font-size: var(--font-size-sm);
  text-transform: uppercase;
  margin-bottom: var(--space-2);
}
.site-footer ul { list-style: none; margin: 0; padding: 0; }
.site-footer li { margin-bottom: var(--space-1); }
.footer-brand-desc { max-width: 280px; }
.site-footer .copyright {
  margin-top: var(--space-6);
  border-top: 1px solid var(--color-border);
  padding-top: var(--space-4);
  text-align: center;
}

/* ---------- Breadcrumb ---------- */
.breadcrumb {
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
  margin: var(--space-4) 0;
}
.breadcrumb a { color: var(--color-secondary); }
.breadcrumb .sep { margin: 0 var(--space-1); color: var(--color-border); }
.breadcrumb .current { color: var(--color-text); }

/* ---------- Hero (v1.1: editorial, left-aligned, paper bg, no gradient) ---------- */
.hero {
  background: var(--color-bg);
  color: var(--color-text);
  padding: var(--space-8) 0 var(--space-7);
  text-align: left;
  border-bottom: 1px solid var(--color-border);
}
.hero .container { max-width: 760px; margin: 0; padding-left: var(--space-4); }
.hero h1 { color: var(--color-primary); }
.hero .eyebrow {
  font-size: var(--font-size-sm);
  font-weight: 600;
  letter-spacing: 0.02em;
  color: var(--color-primary);
  text-transform: uppercase;
  margin: 0 0 var(--space-2);
}
.hero p {
  font-size: var(--font-size-lg);
  color: var(--color-text-muted);
  max-width: 640px;
  margin: var(--space-3) 0 var(--space-5);
}
.hero .hero-actions {
  display: flex;
  gap: var(--space-3);
  flex-wrap: wrap;
}
.hero-btn-secondary { margin-left: 0; }

/* ---------- Buttons (Epic 6: Core Components) ---------- */
.btn {
  display: inline-block;
  padding: var(--space-2) var(--space-5);
  border-radius: var(--radius);
  font-weight: 800;
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  letter-spacing: 0.02em;
  cursor: pointer;
  border: 2px solid transparent;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
}
.btn-primary {
  background: var(--color-accent);
  color: var(--color-white);
}
.btn-primary:hover { background: var(--color-secondary); text-decoration: none; }
.btn-secondary {
  background: transparent;
  border-color: var(--color-primary);
  color: var(--color-primary);
}
.btn-secondary:hover { background: var(--color-bg-alt); text-decoration: none; }
.btn-download {
  background: var(--color-primary);
  color: var(--color-white);
}
.btn-download:hover { background: var(--color-secondary); text-decoration: none; }

/* ---------- Cards (Epic 6: Core Components) ---------- */
.card-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-5);
  margin: var(--space-6) 0;
}
.card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-5);
  background: var(--color-white);
}
.card:hover { border-color: var(--color-text-muted); }
.card h3 { margin-top: 0; font-size: var(--font-size-lg); }
.card p { color: var(--color-text-muted); font-size: var(--font-size-sm); }
.card .card-link { font-weight: 800; font-size: var(--font-size-xs); text-transform: uppercase; }
.card .reading-time {
  display: block;
  font-size: var(--font-size-xs);
  color: var(--color-secondary);
  font-weight: 800;
  text-transform: uppercase;
  margin-bottom: var(--space-2);
}

/* ---------- Value proposition strip (v1.1: lightweight, no shadows) ---------- */
.value-prop-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-6);
  margin: var(--space-6) 0;
}
.value-item h3 {
  font-size: var(--font-size-lg);
  margin-top: 0;
  margin-bottom: var(--space-2);
}
.value-item p {
  color: var(--color-text-muted);
  font-size: var(--font-size-sm);
  margin: 0;
}

/* ---------- Article component (Epic 6: Core Components) ---------- */
.article-meta {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-4);
  align-items: center;
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
  border-bottom: 1px solid var(--color-border);
  padding-bottom: var(--space-4);
  margin-bottom: var(--space-5);
}
.tag {
  display: inline-block;
  background: var(--color-bg-alt);
  color: var(--color-primary);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  padding: 2px 10px;
  font-size: var(--font-size-xs);
  font-weight: 800;
  margin-right: var(--space-1);
}
.article-body { max-width: 720px; }
.article-body p { margin-bottom: var(--space-4); }
.article-body ul, .article-body ol { margin-bottom: var(--space-4); padding-left: var(--space-5); }
.article-body blockquote {
  border-left: 4px solid var(--color-accent);
  margin: var(--space-5) 0;
  padding: var(--space-2) var(--space-5);
  background: var(--color-bg-alt);
  font-style: italic;
  color: var(--color-text-muted);
}
.article-body table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: var(--space-4);
  font-size: var(--font-size-sm);
}
.article-body table th, .article-body table td {
  border: 1px solid var(--color-border);
  padding: var(--space-2) var(--space-3);
  text-align: left;
}
.article-body table th { background: var(--color-bg-alt); }
.article-figure {
  margin: var(--space-6) 0;
}
.article-figure img {
  width: 100%;
  height: auto;
  display: block;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
}
.article-figure figcaption {
  margin-top: var(--space-2);
  font-size: var(--font-size-xs);
  color: var(--color-text-muted);
  text-align: center;
}
.callout {
  border: 1px solid var(--color-border);
  background: var(--color-bg-alt);
  border-radius: var(--radius);
  padding: var(--space-4) var(--space-5);
  margin: var(--space-5) 0;
}
.series-nav {
  display: flex;
  justify-content: space-between;
  gap: var(--space-4);
  margin: var(--space-6) 0 0;
  padding-top: var(--space-5);
  border-top: 1px solid var(--color-border);
  font-size: var(--font-size-sm);
}
.series-nav a { font-weight: 800; }
.series-nav .series-next { text-align: right; margin-left: auto; }
.references {
  margin-top: var(--space-7);
  padding-top: var(--space-5);
  border-top: 1px solid var(--color-border);
  font-size: var(--font-size-sm);
  color: var(--color-text-muted);
}
.references h2 { font-size: var(--font-size-lg); margin-top: 0; }

/* ---------- Category switcher ---------- */
.category-switcher {
  display: flex;
  gap: var(--space-2);
  margin: var(--space-5) 0 var(--space-6);
  flex-wrap: wrap;
}
.category-switcher a {
  padding: var(--space-1) var(--space-4);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  font-size: var(--font-size-sm);
  font-weight: 800;
  color: var(--color-primary);
  min-height: 44px;
  display: inline-flex;
  align-items: center;
}
.category-switcher a.active {
  background: var(--color-primary);
  color: var(--color-white);
  border-color: var(--color-primary);
}
.category-switcher a:hover { text-decoration: none; background: var(--color-bg-alt); }

/* ---------- Resource cards ---------- */
.resource-list {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-5);
  margin: var(--space-6) 0;
}
.resource-card {
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: var(--space-5);
  background: var(--color-white);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}
.resource-card .resource-type {
  font-size: var(--font-size-xs);
  text-transform: uppercase;
  font-weight: 800;
  color: var(--color-secondary);
  letter-spacing: 0.05em;
}

/* ---------- Section helpers ---------- */
.section { padding: var(--space-7) 0; }
.section-alt { background: var(--color-bg-alt); }
.text-center { text-align: center; }
.section-head { margin-bottom: var(--space-5); }
.section-head h2 { margin-top: 0; }
.section-link {
  font-weight: 800;
  font-size: var(--font-size-xs);
  text-transform: uppercase;
}

/* ============================================================
   Responsive breakpoints (Epic 1: Responsive Layout)
   Mobile-first tiers: <640 mobile · 640-1024 tablet ·
   1024-1440 laptop (default styles below) · >1440 large desktop
   ============================================================ */

/* ---- Large desktop: >1440px — expanded content layout ---- */
@media (min-width: 1441px) {
  :root { --max-width: 1200px; }
  .hero .container { max-width: 860px; }
  .article-body { max-width: 780px; }
}

/* ---- Laptop / tablet shared adjustments: <=1024px ---- */
@media (max-width: 1024px) {
  .value-prop-grid { gap: var(--space-5); }
  h1 { font-size: 36px; }        /* tablet: 32-40px */
  html, body { font-size: 17px; line-height: 1.7; }
  .article-body { font-size: 17px; line-height: 1.7; }
}

/* ---- Tablet: 640-1024px — optimized reading layout, 2-col cards ---- */
@media (max-width: 900px) {
  .card-grid { grid-template-columns: repeat(2, 1fr); }
  .value-prop-grid { grid-template-columns: repeat(2, 1fr); }
  .resource-list { grid-template-columns: 1fr; }
}

@media (max-width: 768px) {
  .nav-toggle {
    display: inline-block;
    min-height: 44px;
    min-width: 44px;
  }
  .main-nav {
    display: none;
    width: 100%;
  }
  .main-nav.open { display: block; }
  .main-nav ul {
    flex-direction: column;
    gap: 0;
    padding: var(--space-4) 0;
  }
  .main-nav li { border-top: 1px solid rgba(255,255,255,0.15); }
  .main-nav a {
    display: flex;
    align-items: center;
    min-height: 44px;
    padding: var(--space-2) 0;
  }
  .site-header .container { flex-wrap: wrap; }
  .hero { padding: var(--space-6) 0 var(--space-5); }
  .hero .hero-actions { flex-direction: column; }
  .hero .hero-actions .btn { width: 100%; }
  .btn {
    min-height: 44px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }
  /* Every clickable text link keeps a real touch target on touch devices */
  .card-link, .section-link, .breadcrumb a { display: inline-block; min-height: 44px; line-height: 44px; }
}

/* ---- Mobile: <640px — single-column layout ---- */
@media (max-width: 640px) {
  .container { padding: 0 var(--space-3); }
  .footer-cols { flex-direction: column; }
  .card-grid { grid-template-columns: 1fr; }
  .value-prop-grid { grid-template-columns: 1fr; }
  .resource-list { grid-template-columns: 1fr; }
  .hero .container { padding-left: var(--space-3); }
  h1 { font-size: 30px; }        /* mobile: 28-32px */
  html, body { font-size: 16px; line-height: 1.7; }
  .article-body { font-size: 16px; line-height: 1.7; }
  /* Wide tables (e.g. mistake/fix tables) scroll horizontally instead of
     breaking the page layout or forcing the whole viewport to scroll. */
  .article-body table { display: block; overflow-x: auto; white-space: nowrap; -webkit-overflow-scrolling: touch; }
}