/* The sticky header: logo, navigation, theme button and mobile menu. */

.site-header {
  /* "sticky" keeps the header at the top while the page scrolls under it. */
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid transparent;
  background: var(--color-bg);
  transition: box-shadow 0.2s ease, border-color 0.2s ease;
}

/* js/header-shadow.js adds this class once the page is scrolled a little. */
.site-header.is-scrolled {
  border-bottom-color: var(--color-border);
  box-shadow: var(--shadow-sm);
}

.header-inner {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-height: var(--header-height);
}

.header-inner .logo {
  /* An "auto" margin takes all free space, so the rest moves to the right. */
  margin-right: auto;
}

/* Small screens: the nav is a panel under the header, closed by default. */
.site-nav {
  display: none;
  position: absolute;
  top: 100%;
  right: 0;
  left: 0;
  padding: var(--space-3) var(--space-4) var(--space-4);
  border-bottom: 1px solid var(--color-border);
  background: var(--color-surface);
  box-shadow: var(--shadow-md);
}

/* CSS reads the ARIA attribute. WHY: what you see and what a screen reader
   hears can never disagree, because both come from the same attribute. */
.menu-toggle[aria-expanded="true"] + .site-nav {
  display: block;
}

.nav-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}

.site-nav a {
  display: block;
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-full);
  color: var(--color-text-muted);
  font-weight: 600;
  text-decoration: none;
}

.site-nav a:hover {
  background: var(--color-bg-alt);
  color: var(--color-text);
}

/* js/active-nav.js sets aria-current on the link of the section in view. */
.site-nav a[aria-current] {
  background: var(--color-brand-soft);
  color: var(--color-brand-strong);
}

/* The header button is hidden on phones: the hero has the same links.
   WHY two classes: buttons.css loads later and also sets "display" for .btn.
   Two classes beat one, so this rule wins whatever the file order is. */
.site-header .header-cta {
  display: none;
}

/* Wide screens: the nav sits in the header row and the menu button is gone. */
@media (min-width: 60rem) {
  .site-header .menu-toggle {
    display: none;
  }

  .site-nav {
    display: block;
    position: static;
    padding: 0;
    border: 0;
    background: none;
    box-shadow: none;
  }

  .nav-list {
    flex-direction: row;
  }

  .site-nav a {
    padding: var(--space-2) var(--space-3);
    font-size: var(--text-sm);
  }

  .site-header .header-cta {
    display: inline-flex;
    margin-left: var(--space-2);
  }
}