/**
 * @file css/base.css
 * Base reset, typography, WCAG 2.2 AA accessibility rules, and 3-zone Top Bar Contract.
 */

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* Universal hidden contract to prevent any display override */
[hidden] {
  display: none !important;
}

html {
  font-size: calc(16px * var(--font-scale, 1));
  -webkit-text-size-adjust: 100%;
  color-scheme: dark;
  scroll-behavior: smooth;
}

body {
  min-height: 100vh;
  background-color: var(--bg-canvas);
  background-image: var(--bg-canvas-gradient);
  color: var(--text-primary);
  font-family: var(--font-sans);
  line-height: 1.55;
  letter-spacing: 0.01em;
  overflow-x: hidden;
  display: flex;
  flex-direction: column;
}

/* Focus rings for WCAG 2.2 AA keyboard navigation */
:focus-visible {
  outline: 3px solid var(--accent-primary);
  outline-offset: 3px;
}

/* Skip link for screen readers & keyboard users */
.skip-link {
  position: absolute;
  top: -100px;
  left: var(--space-4);
  background: var(--accent-primary);
  color: var(--text-on-accent);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-sm);
  font-weight: 700;
  z-index: var(--z-panic);
  text-decoration: none;
}

.skip-link:focus {
  top: var(--space-3);
}

/* Screen-reader only utility */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Typography Hierarchy */
h1, h2, h3, h4, .font-display {
  font-family: var(--font-display);
  font-weight: 700;
  line-height: 1.18;
  text-wrap: balance;
}

.tabular-nums {
  font-variant-numeric: tabular-nums;
}

.font-mono {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
}

.font-condensed {
  font-family: var(--font-condensed);
  font-variant-numeric: tabular-nums;
}

a {
  color: inherit;
  text-decoration: none;
}

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

button {
  cursor: pointer;
  background: none;
  border: none;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.45;
}

/* Strict 3-Zone Top Bar Contract */
.top-bar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 2rem;
  padding: 0.875rem 1.5rem;
  background: var(--bg-glass);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border-subtle);
  position: sticky;
  top: 0;
  z-index: var(--z-sticky);
}

.top-bar__brand {
  font-family: var(--font-display);
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--text-primary);
  white-space: nowrap;
  flex-shrink: 0;
}

.top-bar__nav {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  overflow-x: auto;
}

.top-bar__link {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text-secondary);
  white-space: nowrap;
  flex-shrink: 0;
  padding: 0.25rem 0;
  border-bottom: 2px solid transparent;
  transition: color var(--duration-fast) var(--ease-out),
              border-color var(--duration-fast) var(--ease-out);
}

.top-bar__link:hover,
.top-bar__link[aria-current="page"] {
  color: var(--text-primary);
  border-bottom-color: var(--accent-primary);
}

.top-bar__action {
  flex-shrink: 0;
  display: flex;
  align-items: center;
}

/* Main Container */
.container {
  width: 100%;
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-6) var(--space-4);
}

@media (min-width: 768px) {
  .container {
    padding: var(--space-8) var(--space-6);
  }
}

/* Metadata inline text (Zero-Pill Discipline) */
.meta-inline {
  display: flex;
   flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.8125rem;
  color: var(--text-muted);
}

.meta-sep {
  opacity: 0.55;
  user-select: none;
}

/* Hairline Dividers */
.hairline {
  border: 0;
  border-top: 1px solid var(--border-subtle);
  margin: var(--space-6) 0;
}