/**
 * Site navigation.
 *
 * Replaces the legacy raster navigation: a background PNG at a fixed 131px
 * height, absolutely positioned at top:-16px, swapped for two other PNGs across
 * three breakpoints, with line-height:7px under 767px holding it together.
 * None of that scales or recolours, so this is a rebuild rather than a port.
 *
 * Sits below Page Banner in the DOM and on screen. Sticks to the top once the
 * banner scrolls past.
 */

/* ----------------------------------------------------------------------
   Skip link
   ---------------------------------------------------------------------- */

.skip-link {
  position: absolute;
  inset-block-start: 0;
  inset-inline-start: 0;
  z-index: 100;
  padding: var(--space-2xs) var(--space-s);
  background-color: var(--color-surface);
  color: var(--color-brand-strong);
  font-family: var(--font-ui);
  font-size: var(--step-0);
  transform: translateY(-100%);
}

.skip-link:focus {
  transform: translateY(0);
}

/* ----------------------------------------------------------------------
   Shell
   ---------------------------------------------------------------------- */

.site-header {
  --_pad: var(--space-xs);

  position: sticky;
  inset-block-start: 0;
  z-index: 50;
  background-color: var(--color-surface);
  border-block-end: var(--border-width) solid var(--color-border);
}

.site-header__inner {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-s);
  inline-size: 100%;
  max-inline-size: var(--container-wide);
  margin-inline: auto;
}

/* ----------------------------------------------------------------------
   Navigation, wide
   ---------------------------------------------------------------------- */

.site-header__nav {
  display: flex;
  flex: 1 1 auto;
  justify-content: center;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 0 var(--space-m);
  margin: 0;
  padding: 0;
  list-style: none;
}

.site-nav__item {
  display: flex;
}

.site-nav__link {
  display: flex;
  align-items: center;

  /* 44px minimum target. The legacy nav failed this at every breakpoint. */
  min-block-size: 2.75rem;
  padding-block: var(--_pad);
  padding-inline: var(--space-3xs);

  color: var(--color-nav);
  font-family: var(--font-ui);
  font-size: var(--step-0);
  font-weight: var(--weight-medium);
  text-transform: uppercase;
  letter-spacing: var(--tracking-wide);
  text-decoration: none;
  white-space: nowrap;

  border-block-end: 2px solid transparent;
  transition: color var(--duration) var(--easing),
              border-color var(--duration) var(--easing);
}

.site-nav__link:hover {
  color: var(--color-brand-strong);
  border-block-end-color: var(--color-brand-strong);
}

/* ----------------------------------------------------------------------
   Disclosure button
   ---------------------------------------------------------------------- */

.site-header__toggle {
  display: none;
  align-items: center;
  gap: var(--space-2xs);
  min-inline-size: 2.75rem;
  min-block-size: 2.75rem;
  padding: var(--space-3xs) var(--space-2xs);
  border: var(--border-width) solid var(--color-border);
  border-radius: var(--radius);
  background-color: var(--color-surface);
  color: var(--color-nav);
  font-family: var(--font-ui);
  font-size: var(--step--1);
  text-transform: uppercase;
  letter-spacing: var(--tracking-wide);
  cursor: pointer;
}

.site-header__toggle-bars {
  position: relative;
  display: block;
  inline-size: 1.25rem;
  block-size: 2px;
  background-color: currentColor;
}

.site-header__toggle-bars::before,
.site-header__toggle-bars::after {
  content: "";
  position: absolute;
  inset-inline-start: 0;
  display: block;
  inline-size: 1.25rem;
  block-size: 2px;
  background-color: currentColor;
}

.site-header__toggle-bars::before {
  inset-block-start: -6px;
}

.site-header__toggle-bars::after {
  inset-block-start: 6px;
}

/* ----------------------------------------------------------------------
   Narrow
   ---------------------------------------------------------------------- */

@media (max-width: 63.999rem) {

  .site-header__inner {
    flex-wrap: wrap;
    justify-content: flex-end;
    padding-inline: var(--gutter);
  }

  .site-header__toggle {
    display: flex;
  }

  .site-header__nav {
    flex-basis: 100%;
  }

  /* Hidden attribute rather than a class, so the state lives in the DOM where
     assistive technology can see it. */
  .site-header__nav[hidden] {
    display: none;
  }

  .site-nav {
    display: grid;
    gap: 0;
    inline-size: 100%;
  }

  .site-nav__item {
    border-block-start: var(--border-width) solid var(--color-border);
  }

  .site-nav__link {
    padding-block: var(--space-2xs);
    padding-inline: 0;
    border-block-end: none;
  }
}