/* Navbar */
.nav {
  position: sticky; top: 0; z-index: 50; height: var(--nav-h);
  display: flex; align-items: center; justify-content: space-between;
  padding: 0 clamp(16px, 3vw, 32px);
  backdrop-filter: blur(18px) saturate(160%);
  -webkit-backdrop-filter: blur(18px) saturate(160%);
  background: linear-gradient(180deg, rgba(6,6,10,.75), rgba(6,6,10,.55));
  border-bottom: 1px solid var(--line);
}
.nav__brand { display: flex; align-items: center; gap: 12px; }
.nav__mark {
  width: 38px; height: 38px; display: grid; place-items: center;
  background: linear-gradient(180deg, #14141f, #0a0a12);
  border: 1px solid var(--line-2); border-radius: 10px;
  box-shadow: inset 0 1px 0 rgba(255,255,255,.05);
}
.nav__wordmark { display: flex; flex-direction: column; line-height: 1.1; }
.nav__title { font-family: var(--font-display); font-size: 17px; letter-spacing: -.01em; }
.nav__subtitle { font-size: 10.5px; color: var(--gold); letter-spacing: .16em; text-transform: uppercase; }
.nav__links { display: flex; gap: 8px; align-items: center; }
.nav__links a { padding: 8px 14px; border-radius: 999px; color: var(--ink-1); font-size: 14.5px; transition: color var(--dur-1) var(--ease), background var(--dur-1) var(--ease); }
.nav__links a:hover { color: #fff; background: rgba(255,255,255,.04); }
.nav__toggle { display: none; width: 40px; height: 40px; border-radius: 10px; border: 1px solid var(--line-2); }
.nav__toggle span { display: block; height: 1.5px; background: var(--ink-1); margin: 5px auto; width: 18px; }

@media (max-width: 820px) {
  .nav__links { display: none; }
  .nav__toggle { display: block; }
  .nav__links.is-open {
    display: flex; position: absolute; top: 100%; left: 0; right: 0;
    flex-direction: column; gap: 0; padding: 12px;
    background: rgba(6,6,10,.98); border-bottom: 1px solid var(--line);
  }
  .nav__links.is-open a { padding: 12px 14px; border-radius: 8px; width: 100%; }
}

/* Buttons */
.btn {
  display: inline-flex; align-items: center; gap: 8px;
  padding: 12px 18px; border-radius: 999px;
  font-size: 14.5px; font-weight: 500; letter-spacing: .01em;
  transition: transform var(--dur-1) var(--ease), background var(--dur-2) var(--ease), box-shadow var(--dur-2) var(--ease), color var(--dur-1) var(--ease);
  border: 1px solid transparent; will-change: transform;
}
.btn:active { transform: translateY(1px) scale(.99); }
.btn--primary {
  background: linear-gradient(180deg, #ffd76a, #f5c24c 40%, #e39a1c);
  color: #1a1300; box-shadow: var(--glow-gold);
}
.btn--primary:hover { box-shadow: 0 0 0 1px rgba(245,194,76,.6), 0 16px 40px -10px rgba(245,194,76,.55); }
.btn--ghost {
  background: rgba(255,255,255,.03); color: var(--ink-0);
  border-color: var(--line-2);
}
.btn--ghost:hover { background: rgba(255,255,255,.06); border-color: #3a3a52; }
.btn--java {
  background: linear-gradient(180deg, #ff9451, #f27522 45%, #c95a0e);
  color: #1a0800; box-shadow: var(--glow-java);
}
.btn--sm { padding: 8px 12px; font-size: 13px; }
.btn--icon { padding: 8px; width: 36px; height: 36px; justify-content: center; }

/* Chip / tab */
.chip {
  padding: 8px 14px; border-radius: 999px; font-size: 13px;
  color: var(--ink-1); background: rgba(255,255,255,.03);
  border: 1px solid var(--line-2);
  transition: all var(--dur-1) var(--ease);
}
.chip:hover { color: #fff; border-color: #3a3a52; }
.chip.is-active {
  color: #1a1300;
  background: linear-gradient(180deg, #ffd76a, #f5c24c);
  border-color: transparent;
  box-shadow: 0 6px 16px -6px rgba(245,194,76,.55);
}

/* Glass panel */
.panel {
  background: linear-gradient(180deg, rgba(20,20,30,.7), rgba(12,12,20,.55));
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: var(--shadow-1);
}
.panel__head {
  display: flex; align-items: center; justify-content: space-between;
  padding: 12px 14px; border-bottom: 1px solid var(--line);
}
.panel__title { font-size: 12px; text-transform: uppercase; letter-spacing: .16em; color: var(--ink-2); }
.panel__body { padding: 14px; }

/* Footer */
.footer { margin-top: 100px; border-top: 1px solid var(--line); background: rgba(6,6,10,.6); }
.footer__inner {
  max-width: var(--container); margin: 0 auto; padding: 28px clamp(16px, 3vw, 32px);
  display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 16px;
}
.footer__brand { font-family: var(--font-display); font-size: 18px; }
.footer__sub { color: var(--ink-2); font-size: 13px; }
.footer__meta { color: var(--ink-2); font-size: 13px; }

/* Difficulty badge */
.diff { display: inline-flex; align-items: center; gap: 6px; padding: 3px 9px; border-radius: 999px; font-size: 11px; font-weight: 600; letter-spacing: .04em; text-transform: uppercase; border: 1px solid; }
.diff--easy { color: var(--diff-easy); border-color: rgba(34,197,94,.35); background: rgba(34,197,94,.08); }
.diff--med  { color: var(--diff-med);  border-color: rgba(245,194,76,.4); background: rgba(245,194,76,.08); }
.diff--hard { color: var(--diff-hard); border-color: rgba(239,68,68,.4);  background: rgba(239,68,68,.08); }