/* Shared styles for every page. No external fonts or CDNs (school web filters). */

:root {
  /* Warm "jotter paper" background with white cards on top */
  --bg: #f5f3ed;
  --surface: #ffffff;
  --text: #17203a;
  --muted: #4c536b;
  --border: #d9d4c7;
  --lift: #cfc9ba;            /* the solid edge under cards and buttons */
  --grid: rgba(23, 32, 58, 0.06);
  --accent: #1f4fd1;
  --accent-text: #ffffff;
  --radius: 10px;
  --tap: 44px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  /* Avenir Next ships with every iPad; other devices fall back to their system font */
  --font-head: "Avenir Next", Avenir, "Segoe UI Variable Display", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, Helvetica, Arial, sans-serif;

  /* Header bar: dark ink in both themes */
  --ink: #16233f;
  --ink-2: #22335a;
  --ink-text: #ffffff;
  --ink-muted: #b9c3dc;

  /* Feedback: blue-green vs amber stays distinct for red/green colour blindness,
     and always comes with words, so colour is never the only cue */
  --good: #0f766e;
  --good-bg: #e6f4f1;
  --bad: #b45309;
  --bad-bg: #fdf1e3;

  /* One colour per level, all paired with a text label so colour is never the only cue */
  --bge: #0f766e;
  --n4: #6d28d9;
  --n5: #1f4fd1;
  --higher: #b45309;
  --ah: #be185d;
  --on-level: #ffffff;        /* text on a filled level colour */

  /* Brighter level colours for the dark header bar (same in both themes) */
  --bge-bright: #2dd4bf;
  --n4-bright: #b49cfc;
  --n5-bright: #8fb0ff;
  --higher-bright: #fbbf24;
  --ah-bright: #f68cc4;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #10131d;
    --surface: #1a1e2c;
    --text: #eef0f7;
    --muted: #aab1cc;
    --border: #2e3448;
    --lift: #0a0c13;
    --grid: rgba(238, 240, 247, 0.05);
    --accent: #8fb0ff;
    --accent-text: #10131d;
    --ink: #0b0e17;
    --ink-2: #1c2235;
    --good: #2dd4bf;
    --good-bg: #10302d;
    --bad: #fbbf24;
    --bad-bg: #3a2a0c;
    --bge: #2dd4bf;
    --n4: #b49cfc;
    --n5: #8fb0ff;
    --higher: #fbbf24;
    --ah: #f68cc4;
    --on-level: #10131d;
  }
}

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

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

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font);
  font-size: 1.125rem;
  line-height: 1.5;
}

h1, h2, h3 { font-family: var(--font-head); font-weight: 700; }

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

.wrap {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 20px;
}

/* Level colour lookup: any element with data-level sets --level-colour for its children */
[data-level="bge"]    { --level-colour: var(--bge);    --level-bright: var(--bge-bright); }
[data-level="n4"]     { --level-colour: var(--n4);     --level-bright: var(--n4-bright); }
[data-level="n5"]     { --level-colour: var(--n5);     --level-bright: var(--n5-bright); }
[data-level="higher"] { --level-colour: var(--higher); --level-bright: var(--higher-bright); }
[data-level="ah"]     { --level-colour: var(--ah);     --level-bright: var(--ah-bright); }

/* Header: brand on the left, one big button per level on the right */
.site-header {
  background: var(--ink);
  color: var(--ink-text);
  border-bottom: 1px solid var(--ink-2);
}
.site-header .wrap {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px 24px;
  padding-top: 12px;
  padding-bottom: 12px;
}
.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  min-height: var(--tap);
  font-family: var(--font-head);
  font-weight: 700;
  font-size: 1.35rem;
  color: var(--ink-text);
  text-decoration: none;
  letter-spacing: -0.01em;
}
.brand span { color: var(--ink-muted); font-weight: 500; }
.brand svg { width: 34px; height: 22px; flex: none; }

.level-nav ul {
  display: flex;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.level-nav a {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 64px;
  min-height: 48px;
  padding: 6px 16px;
  border-radius: var(--radius);
  background: var(--ink-2);
  box-shadow: inset 0 -4px 0 var(--level-bright);
  color: var(--ink-text);
  font-family: var(--font-head);
  font-size: 1.05rem;
  font-weight: 700;
  text-decoration: none;
  -webkit-tap-highlight-color: transparent;
  touch-action: manipulation;
}
.level-nav a[aria-current="page"] {
  background: var(--level-bright);
  box-shadow: none;
  color: var(--ink);
}
.level-nav a:active { transform: translateY(2px); }
@media (max-width: 640px) {
  .level-nav { flex: 1 1 100%; }
  .level-nav a { min-width: 0; padding: 6px 4px; }
  .level-nav li { flex: 1; }
}

/* Page title panel, on faint squared paper */
.hero {
  margin: 24px 0 8px;
  padding: 32px 28px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background-color: var(--surface);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 24px 24px;
  background-position: -1px -1px;
  border-left: 8px solid var(--level-colour, var(--ink));
}
.hero h1 {
  font-size: clamp(2rem, 5vw, 3rem);
  line-height: 1.1;
  letter-spacing: -0.02em;
  margin: 0 0 10px;
}
.hero p {
  color: var(--muted);
  font-size: 1.25rem;
  max-width: 40em;
  margin: 0;
}

/* Cards and buttons share a solid bottom edge, so they look pressable */
.level,
.unit,
.starter-link {
  border: 1px solid var(--border);
  box-shadow: 0 3px 0 var(--lift);
}

/* Level cards (home page) */
.levels {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 18px;
  padding: 24px 0 56px;
  margin: 0;
  list-style: none;
}
.level {
  display: flex;
  align-items: stretch;
  gap: 18px;
  height: 100%;
  min-height: var(--tap);
  padding: 18px;
  background: var(--surface);
  border-radius: var(--radius);
  color: var(--text);
  text-decoration: none;
  -webkit-tap-highlight-color: transparent;
}
a.level:active { transform: translateY(3px); box-shadow: 0 0 0 var(--lift); }
.level-badge {
  display: flex;
  align-items: center;
  justify-content: center;
  flex: none;
  width: 76px;
  border-radius: 8px;
  background: var(--level-colour, var(--accent));
  color: var(--on-level);
  font-family: var(--font-head);
  font-size: 1.6rem;
  font-weight: 700;
  letter-spacing: -0.02em;
}
.level-body { display: flex; flex-direction: column; gap: 4px; }
.level h2 { margin: 0; font-size: 1.45rem; line-height: 1.2; }
.level .stage { color: var(--muted); font-size: 1.05rem; }
.level .status {
  margin-top: auto;
  padding-top: 8px;
  font-size: 1rem;
  font-weight: 700;
  color: var(--level-colour, var(--accent));
}

/* Breadcrumb (starter pages): each step is a button-sized link */
.crumbs {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  margin: 20px 0 0;
  padding: 0;
  list-style: none;
  font-size: 1rem;
}
.crumbs li { display: flex; align-items: center; gap: 8px; min-height: var(--tap); color: var(--muted); }
.crumbs li + li::before { content: "›"; font-size: 1.3rem; line-height: 1; }
.crumbs a {
  display: inline-flex;
  align-items: center;
  min-height: var(--tap);
  padding: 6px 14px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: 0 2px 0 var(--lift);
  color: var(--text);
  font-weight: 600;
  text-decoration: none;
}
.crumbs a:active { transform: translateY(2px); box-shadow: none; }

/* Level page: one section per unit */
.unit {
  margin: 0 0 20px;
  padding: 22px;
  background: var(--surface);
  border-radius: var(--radius);
}
.unit h2 { margin: 0; font-size: 1.5rem; }
.unit-num {
  display: table;
  margin-bottom: 6px;
  padding: 2px 10px;
  border-radius: 6px;
  background: var(--level-colour, var(--accent));
  color: var(--on-level);
  font-family: var(--font);
  font-size: 0.85rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}
.unit-topics { margin: 6px 0 0; color: var(--muted); font-size: 1rem; }
.unit .empty { margin: 14px 0 0; color: var(--muted); font-style: italic; }
.units { padding: 16px 0 48px; }

.starter-list {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
  gap: 12px;
  margin: 16px 0 0;
  padding: 0;
  list-style: none;
}
.starter-link {
  display: flex;
  flex-direction: column;
  gap: 2px;
  height: 100%;
  min-height: var(--tap);
  padding: 14px 16px;
  border-left: 6px solid var(--level-colour, var(--accent));
  border-radius: var(--radius);
  background: var(--bg);
  color: var(--text);
  text-decoration: none;
  -webkit-tap-highlight-color: transparent;
}
.starter-link:active { transform: translateY(3px); box-shadow: 0 0 0 var(--lift); }
.starter-link strong { font-family: var(--font-head); font-size: 1.2rem; }
.starter-link span { color: var(--muted); font-size: 0.95rem; }

/* Footer */
.site-footer {
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 1rem;
  padding: 24px 0 40px;
}

/* Generic centred message page (404 etc.) */
.message {
  padding: 80px 0;
  text-align: center;
}
.message h1 { font-size: 2.5rem; margin: 0 0 12px; }
.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: var(--tap);
  min-width: var(--tap);
  padding: 10px 22px;
  border-radius: var(--radius);
  background: var(--accent);
  color: var(--accent-text);
  font-weight: 600;
  text-decoration: none;
}