/* =============================================================================
   WCAG 2.2 Demo Suite - base design system
   -----------------------------------------------------------------------------
   This stylesheet is itself a teaching artifact. Every rule below exists to
   satisfy a specific success criterion, and the criterion is named in a comment.
   If you change a value here, re-run `npm run test:a11y` and the contrast check.
   ============================================================================= */

/* --- Design tokens ---------------------------------------------------------
   All colour pairs used for text are verified by tools/check-contrast.mjs.
   Light theme targets 7:1 for body text (1.4.6 AAA), never below 4.5:1 (1.4.3). */
:root {
  color-scheme: light dark;

  --bg: #ffffff;
  --surface: #f2f5f8;
  --surface-raised: #ffffff;
  --text: #14171c;
  --text-muted: #444c55;
  --border: #b9c2cb;
  --border-strong: #6d7883;

  --accent: #0a4f9e;
  --accent-hover: #073c79;
  --on-accent: #ffffff;

  --fail: #94101c;
  --fail-bg: #fdf1f2;
  --fail-border: #d4636e;

  --pass: #0f5533;
  --pass-bg: #eef8f2;
  --pass-border: #4c9871;

  --note: #704303;
  --note-bg: #fdf5e8;
  --note-border: #c39445;

  --focus: #0a4f9e;
  --focus-offset: #ffffff;

  --level-a: #1f4e79;
  --level-aa: #603792;
  --level-aaa: #763e06;

  /* Spacing scale in rem so it grows with the user's font size (1.4.4) */
  --sp-1: 0.25rem;
  --sp-2: 0.5rem;
  --sp-3: 0.75rem;
  --sp-4: 1rem;
  --sp-5: 1.5rem;
  --sp-6: 2rem;
  --sp-7: 3rem;

  --radius: 6px;
  --measure: 70ch;          /* 1.4.8 AAA: no more than 80 characters per line */
  --font-body: system-ui, -apple-system, "Segoe UI", Roboto, "Noto Sans", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "Cascadia Mono", Consolas, monospace;
  /* Bangla text (3.1.1 / 3.1.2 demos) needs a font stack that actually has the glyphs */
  --font-bangla: "Noto Sans Bengali", "Nirmala UI", "Vrinda", "Shonar Bangla", sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #12161b;
    --surface: #1a1f26;
    --surface-raised: #222831;
    --text: #edf1f5;
    --text-muted: #b3bec9;
    --border: #3a434e;
    --border-strong: #7d8894;

    --accent: #7fb8f5;
    --accent-hover: #a8cffa;
    --on-accent: #0d1117;

    --fail: #ff9aa4;
    --fail-bg: #2a1619;
    --fail-border: #8f3b45;

    --pass: #86dcae;
    --pass-bg: #12241b;
    --pass-border: #3d7a58;

    --note: #ecc07a;
    --note-bg: #2a2113;
    --note-border: #8a6a2f;

    --focus: #ffd54a;
    --focus-offset: #12161b;

    --level-a: #8fc0ec;
    --level-aa: #cbb0f1;
    --level-aaa: #edb073;
  }
}

/* --- Reset and base --------------------------------------------------------- */
*, *::before, *::after { box-sizing: border-box; }

html {
  /* Never set a px font-size on html: it breaks the user's browser font setting (1.4.4) */
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 1.0625rem;
  /* 1.4.8 AAA: line height at least 1.5 within paragraphs */
  line-height: 1.6;
  /* 1.4.8 AAA: never fully justify - it creates rivers that disrupt tracking */
  text-align: left;
  overflow-wrap: break-word;
}

/* 1.4.12 Text Spacing: no fixed heights on text containers, so user overrides
   for line-height, letter-spacing and word-spacing cannot clip content. */
p, li, dd, dt, blockquote, figcaption, td, th, label, summary {
  max-width: var(--measure);
}
p { margin: 0 0 var(--sp-4); }

h1, h2, h3, h4, h5, h6 {
  line-height: 1.25;
  margin: var(--sp-6) 0 var(--sp-3);
  max-width: var(--measure);
  text-wrap: balance;
}
h1 { font-size: clamp(1.75rem, 1.3rem + 2vw, 2.5rem); margin-top: 0; }
h2 { font-size: clamp(1.4rem, 1.15rem + 1.1vw, 1.8rem); }
h3 { font-size: 1.25rem; }
h4 { font-size: 1.0625rem; }

:is(h1, h2, h3, h4) + * { margin-top: 0; }

img, svg, video, canvas, iframe { max-width: 100%; }
img, video { height: auto; }

/* --- Links ------------------------------------------------------------------
   1.4.1 Use of Color: links in body text are underlined, never colour alone. */
a {
  color: var(--accent);
  text-underline-offset: 0.15em;
  text-decoration-thickness: max(1px, 0.06em);
}
a:hover { color: var(--accent-hover); text-decoration-thickness: max(2px, 0.12em); }

/* --- Focus -------------------------------------------------------------------
   2.4.7 Focus Visible, 2.4.13 Focus Appearance (AAA), 1.4.11 Non-text Contrast.
   A 3px solid outline with a 2px offset exceeds the 2px-perimeter minimum and
   holds >=3:1 against both light and dark backgrounds. Never remove this. */
:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 2px;
  border-radius: 2px;
}
/* Older engines without :focus-visible still get an indicator. */
:focus:not(:focus-visible) { outline: none; }

/* --- Skip link (2.4.1 Bypass Blocks) -----------------------------------------
   Moved off-screen rather than display:none, so it stays focusable. */
.skip-link {
  position: absolute;
  left: var(--sp-3);
  top: var(--sp-3);
  z-index: 100;
  transform: translateY(-200%);
  background: var(--accent);
  color: var(--on-accent);
  padding: var(--sp-3) var(--sp-4);
  border-radius: var(--radius);
  font-weight: 600;
  text-decoration: none;
}
.skip-link:focus { transform: translateY(0); }

/* --- Visually hidden, but available to assistive technology ------------------ */
.visually-hidden {
  position: absolute !important;
  width: 1px; height: 1px;
  padding: 0; margin: -1px;
  overflow: hidden;
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

/* --- Layout ------------------------------------------------------------------
   1.4.10 Reflow: everything is fluid; nothing has a min-width that would force
   horizontal scrolling at a 320px viewport. */
.page {
  width: min(72rem, 100% - 2rem);
  margin-inline: auto;
  padding-block: var(--sp-6) var(--sp-7);
}
.prose { max-width: var(--measure); }

.site-header {
  border-bottom: 2px solid var(--border);
  background: var(--surface);
}
.site-header__inner {
  width: min(72rem, 100% - 2rem);
  margin-inline: auto;
  display: flex;
  flex-wrap: wrap;                 /* wraps instead of overflowing at 320px */
  gap: var(--sp-3) var(--sp-5);
  align-items: center;
  padding-block: var(--sp-3);
}
.site-header__title {
  font-size: 1.0625rem;
  font-weight: 700;
  margin: 0;
}
.site-header__title a {
  display: inline-flex;
  align-items: center;
  gap: var(--sp-3);
  color: var(--text);
  text-decoration: none;
}
.site-header__title a:hover { text-decoration: underline; }
.site-header__logo {
  height: 2rem;
  width: 2rem;
  border-radius: 4px;
}

.site-nav ul {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2) var(--sp-4);
  margin: 0;
  padding: 0;
}
/* 3.2.3 Consistent Navigation: this markup is identical on every page, and
   2.4.8 Location: the current page is marked with aria-current, not colour alone. */
.site-nav a[aria-current="page"] {
  font-weight: 700;
  text-decoration-thickness: max(2px, 0.12em);
}

.site-footer {
  border-top: 2px solid var(--border);
  background: var(--surface);
  margin-top: var(--sp-7);
  padding-block: var(--sp-5);
  color: var(--text-muted);
}
.site-footer__inner {
  width: min(72rem, 100% - 2rem);
  margin-inline: auto;
}

/* --- Breadcrumbs (2.4.8 Location) -------------------------------------------- */
.breadcrumb ol {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: var(--sp-2);
  margin: 0 0 var(--sp-5);
  padding: 0;
  font-size: 0.9375rem;
  color: var(--text-muted);
}
.breadcrumb li + li::before {
  content: "/";
  margin-right: var(--sp-2);
  color: var(--border-strong);
}

/* --- Buttons and controls ----------------------------------------------------
   2.5.8 Target Size (Minimum): min 24x24 CSS px. These exceed it at 44px to
   also satisfy 2.5.5 Target Size (Enhanced) at AAA. */
.button, button.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--sp-2);
  min-height: 44px;
  min-width: 44px;
  padding: var(--sp-2) var(--sp-4);
  border: 2px solid var(--accent);
  border-radius: var(--radius);
  background: var(--accent);
  color: var(--on-accent);
  font: inherit;
  font-weight: 600;
  text-decoration: none;
  cursor: pointer;
}
.button:hover { background: var(--accent-hover); border-color: var(--accent-hover); color: var(--on-accent); }
.button--secondary {
  background: transparent;
  color: var(--accent);
}
.button--secondary:hover { background: var(--surface); color: var(--accent-hover); }

/* Form controls used by the filter UI and worksheets.
   1.4.11 Non-text Contrast: borders are >=3:1 against the page background. */
input, select, textarea {
  font: inherit;
  color: var(--text);
  background: var(--surface-raised);
  border: 2px solid var(--border-strong);
  border-radius: var(--radius);
  padding: var(--sp-2) var(--sp-3);
  min-height: 44px;
  max-width: 100%;
}
textarea { min-height: 6rem; line-height: 1.6; }
label { display: inline-block; font-weight: 600; margin-bottom: var(--sp-1); }

/* --- Level badges ------------------------------------------------------------
   1.4.1 Use of Color: the level is spelled out in text, not signalled by colour. */
.level {
  display: inline-block;
  border: 2px solid currentColor;
  border-radius: 999px;
  padding: 0 var(--sp-2);
  font-size: 0.8125rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  white-space: nowrap;
}
.level--A { color: var(--level-a); }
.level--AA { color: var(--level-aa); }
.level--AAA { color: var(--level-aaa); }
.level--OBSOLETE { color: var(--text-muted); }

/* --- Callouts ----------------------------------------------------------------
   Each uses an icon glyph plus a text prefix, never colour alone (1.4.1). */
.callout {
  border: 2px solid var(--border);
  border-left-width: 6px;
  border-radius: var(--radius);
  background: var(--surface);
  padding: var(--sp-4);
  margin: var(--sp-5) 0;
  max-width: var(--measure);
}
.callout > :last-child { margin-bottom: 0; }
.callout__title { font-weight: 700; margin: 0 0 var(--sp-2); display: flex; gap: var(--sp-2); }
.callout--fail { border-color: var(--fail-border); background: var(--fail-bg); }
.callout--fail .callout__title { color: var(--fail); }
.callout--pass { border-color: var(--pass-border); background: var(--pass-bg); }
.callout--pass .callout__title { color: var(--pass); }
.callout--note { border-color: var(--note-border); background: var(--note-bg); }
.callout--note .callout__title { color: var(--note); }

/* --- Tables ------------------------------------------------------------------
   1.4.10 Reflow exempts data tables from the no-horizontal-scroll rule, but the
   scroll container must be keyboard reachable, so it carries tabindex="0"
   (see the scrollable-region-focusable axe rule under 2.1.1). */
.table-scroll {
  overflow-x: auto;
  margin: var(--sp-5) 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.table-scroll:focus-visible { outline: 3px solid var(--focus); outline-offset: -3px; }
table { border-collapse: collapse; width: 100%; }
caption { text-align: left; font-weight: 700; padding: var(--sp-3); }
th, td {
  text-align: left;
  padding: var(--sp-3);
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}
thead th { background: var(--surface); border-bottom: 2px solid var(--border-strong); }

/* --- Code --------------------------------------------------------------------
   Exempt from reflow, so it scrolls horizontally inside its own container. */
pre {
  overflow-x: auto;
  /* Without max-width the <pre> reports its full content width as its intrinsic
     size, which propagates up through grid and flex parents (see .panel in
     demo.css) and breaks 1.4.10 Reflow. */
  max-width: 100%;
  background: var(--surface);
  border: 1px solid var(--border);
  border-left: 6px solid var(--border-strong);
  border-radius: var(--radius);
  padding: var(--sp-4);
  margin: var(--sp-4) 0;
  line-height: 1.55;
}
pre:focus-visible { outline: 3px solid var(--focus); outline-offset: -3px; }
code { font-family: var(--font-mono); font-size: 0.9375em; }
:not(pre) > code {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 3px;
  padding: 0.1em 0.35em;
}

/* --- Bangla passages (3.1.1 / 3.1.2 demos) ----------------------------------- */
[lang="bn"] {
  font-family: var(--font-bangla);
  line-height: 1.85;   /* Bangla needs more leading than Latin at the same size */
}

/* --- Motion ------------------------------------------------------------------
   2.3.3 Animation from Interactions (AAA) and 2.2.2 Pause, Stop, Hide.
   Motion is removed rather than merely shortened. */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
}

/* --- Windows High Contrast / forced colours ---------------------------------- */
@media (forced-colors: active) {
  .button { border: 2px solid ButtonText; }
  :focus-visible { outline: 3px solid Highlight; }
  .level { border-color: CanvasText; }
}