/* ───────────────────────────────────────────────────────────────────────
   shared/nav.css — canonical public top-nav (MRB-109)

   Single source of truth for the public/student-facing nav across the whole
   site: the 997 generated topic pages, the homepage, and the hand-written
   app pages (leaderboard, weekly-challenge, my-challenges, past-papers,
   profile-setup, revision).

   Layout: brand/wordmark on the LEFT (links home) + optional breadcrumb;
   a compact utility cluster on the RIGHT (Challenge pill, Leaderboard,
   Search, auth control) that is persistent at all widths; and a hamburger
   button that opens a full-menu drawer. Behaviour + accessibility live in
   shared/nav.js. Tokens only — no new colours.

   Dashboards (teacher/*, student/*, teacher-profile) keep their own
   utilitarian .top-nav per the brand rule and do NOT load this file.
   ─────────────────────────────────────────────────────────────────────── */

.nav {
  background: var(--card);
  border-bottom: 1px solid var(--border);
  padding: 0 var(--sp-5);
  height: 62px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--sp-3);
  position: sticky;
  top: 0;
  z-index: 100;
}

/* ── Brand / wordmark (left) ── */
.nav-brand {
  font-family: var(--font-serif);
  font-optical-sizing: auto;
  font-size: 1.35rem;
  font-weight: 600;
  color: var(--text);
  letter-spacing: -0.01em;
  display: flex;
  align-items: center;
  gap: 9px;
  text-decoration: none;
  flex-shrink: 0;
}
.brand-logo { flex-shrink: 0; }

/* ── Optional breadcrumb (left, after brand; hidden on narrow screens) ── */
.nav-crumbs { display: flex; align-items: center; gap: 6px; min-width: 0; overflow: hidden; }
.nav-crumbs .crumb-sep { color: var(--border-strong); font-size: 0.8rem; }
.nav-crumbs a.crumb {
  font-size: var(--fs-small);
  font-weight: 700;
  text-decoration: none;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* ── Utility cluster (right) — persistent at all widths ── */
.nav-cluster { display: flex; align-items: center; gap: var(--sp-1); flex-shrink: 0; }

.nav-cluster a { text-decoration: none; }

.challenge-chip {
  color: var(--on-accent);
  background: var(--accent);
  font-weight: 700;
  font-size: var(--fs-small);
  padding: 7px 15px;
  border-radius: 999px;
  white-space: nowrap;
  transition: background 0.15s;
}
.challenge-chip:hover { background: var(--accent-hover); color: var(--on-accent); }

.nav-icon-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 1.05rem;
  line-height: 1;
  color: var(--muted);
  padding: 7px 10px;
  border-radius: 999px;
  transition: background 0.15s, color 0.15s;
}
.nav-icon-link:hover { background: var(--accent-soft); color: var(--accent); }

/* Auth control — Sign In / Sign Up when signed out, chip when signed in.
   The chip colours are the audited ~5.5:1 contrast pair — do not weaken. */
#nav-auth-area { display: flex; gap: 6px; align-items: center; }
.btn-signup {
  border: 1.5px solid var(--accent);
  color: var(--accent);
  padding: 6px 15px;
  border-radius: 999px;
  font-weight: 700;
  font-size: var(--fs-small);
  white-space: nowrap;
}
.btn-signup:hover { background: var(--accent-soft); color: var(--accent); }
.btn-signin {
  background: var(--accent);
  color: var(--on-accent);
  padding: 7px 16px;
  border-radius: 999px;
  font-weight: 700;
  font-size: var(--fs-small);
  white-space: nowrap;
}
.btn-signin:hover { background: var(--accent-hover); color: var(--on-accent); }

/* ── Hamburger button ── */
.nav-burger {
  display: inline-flex;
  flex-direction: column;
  justify-content: center;
  gap: 4px;
  width: 40px;
  height: 38px;
  padding: 0 9px;
  background: none;
  border: 1px solid var(--border);
  border-radius: 10px;
  cursor: pointer;
  flex-shrink: 0;
  transition: background 0.15s, border-color 0.15s;
}
.nav-burger:hover { background: var(--accent-soft); border-color: var(--accent-border); }
.nav-burger span {
  display: block;
  height: 2px;
  width: 100%;
  background: var(--text);
  border-radius: 2px;
  transition: transform 0.2s, opacity 0.2s;
}
.nav-burger[aria-expanded="true"] span:nth-child(1) { transform: translateY(6px) rotate(45deg); }
.nav-burger[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-burger[aria-expanded="true"] span:nth-child(3) { transform: translateY(-6px) rotate(-45deg); }
.nav-burger:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

/* ── Drawer + scrim (injected by nav.js) ── */
.nav-overlay {
  position: fixed;
  inset: 0;
  background: rgba(20, 14, 8, 0.44);
  opacity: 0;
  visibility: hidden;
  transition: opacity 0.2s ease, visibility 0.2s ease;
  z-index: 200;
}
.nav-overlay.open { opacity: 1; visibility: visible; }

.nav-drawer {
  position: fixed;
  top: 0;
  right: 0;
  height: 100%;
  width: min(320px, 85vw);
  background: var(--card);
  border-left: 1px solid var(--border);
  box-shadow: var(--shadow-pop);
  transform: translateX(100%);
  transition: transform 0.24s ease;
  z-index: 201;
  display: flex;
  flex-direction: column;
  padding: 18px 16px calc(18px + env(safe-area-inset-bottom));
  overflow-y: auto;
}
.nav-drawer.open { transform: translateX(0); }

.nav-drawer-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 10px;
}
.nav-drawer-title {
  font-family: var(--font-serif);
  font-optical-sizing: auto;
  font-weight: 600;
  font-size: 1.05rem;
  color: var(--text);
}
.nav-drawer-close {
  background: none;
  border: none;
  color: var(--muted);
  font-size: 1.4rem;
  line-height: 1;
  cursor: pointer;
  padding: 4px 8px;
  border-radius: 8px;
}
.nav-drawer-close:hover { background: var(--sunken); color: var(--text); }
.nav-drawer-close:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.nav-drawer-menu { display: flex; flex-direction: column; gap: 2px; margin-top: 4px; }
.nav-drawer-menu a,
.nav-drawer-menu button.nav-drawer-link {
  display: flex;
  align-items: center;
  gap: 12px;
  width: 100%;
  text-align: left;
  background: none;
  border: none;
  font-family: var(--font-sans);
  font-size: 1rem;
  font-weight: 600;
  color: var(--text);
  text-decoration: none;
  padding: 13px 12px;
  border-radius: 10px;
  cursor: pointer;
}
.nav-drawer-menu a:hover,
.nav-drawer-menu button.nav-drawer-link:hover { background: var(--accent-soft); color: var(--accent); }
.nav-drawer-menu a:focus-visible,
.nav-drawer-menu button.nav-drawer-link:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.nav-drawer-menu .nav-drawer-ico { font-size: 1.1rem; width: 22px; text-align: center; flex-shrink: 0; }

.nav-drawer-auth {
  margin-top: auto;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.nav-drawer-auth a,
.nav-drawer-auth .nav-drawer-chip {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 12px 14px;
  border-radius: 999px;
  font-weight: 700;
  font-size: 0.95rem;
  text-decoration: none;
  white-space: nowrap;
}

/* ── Responsive tightening ── */
@media (max-width: 900px) { .nav-crumbs { display: none; } }
@media (max-width: 560px) {
  .nav { padding: 0 var(--sp-3); gap: var(--sp-2); }
  .nav-brand { font-size: 1.1rem; gap: 7px; }
  .nav-cluster { gap: 3px; }
  .challenge-chip .nav-chip-label { display: none; }   /* ⚡ only on small screens */
  .challenge-chip { padding: 7px 9px; }
  .nav-icon-link { padding: 6px 7px; }
  /* Sign Up collapses into the drawer on phones so the persistent cluster
     (Challenge, Leaderboard, Search, Sign In, menu) fits without overflow.
     The signed-in chip is a single element and is unaffected. */
  #nav-auth-area .btn-signup { display: none; }
  .btn-signin { padding: 7px 12px; }
  .nav-burger { width: 36px; padding: 0 8px; }
}
/* Smallest phones: Leaderboard + Search collapse into the drawer so the bar
   never overflows. Challenge (primary CTA), Sign In and the menu stay put. */
@media (max-width: 400px) {
  .nav-cluster .nav-icon-link { display: none; }
}
@media (max-width: 360px) {
  .nav-brand { font-size: 1rem; }
}