:root {
  --bg: #0f1115;
  --panel: #161a22;
  --accent: #00ff99;
  --accent-2: #00aaff;
  --text: #e8eef8;
  --muted: #9aa4b2;
  --shadow: 0 6px 18px rgba(0,0,0,.35);
  --radius: 14px;
  --card-size: 96px;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: ui-sans-serif, system-ui, "Segoe UI", Roboto, Arial, sans-serif;
  background: radial-gradient(1200px 800px at 20% -20%, #132, transparent),
              radial-gradient(1200px 800px at 120% 20%, #123, transparent),
              var(--bg);
  color: var(--text);
}

.app-header {
  padding: 24px 16px 8px;
  text-align: center;
}
h1 {
  margin: 0 0 8px;
  font-size: clamp(1.4rem, 2.6vw, 2.2rem);
  letter-spacing: .5px;
  display: inline-flex;
  align-items: center;
  gap: .6rem;
}
.logo { filter: drop-shadow(0 4px 10px rgba(0,0,0,.5)); }

#timerContainer {
  color: var(--muted);
  font-weight: 600;
}

main { display: grid; place-items: center; padding: 16px; }

.board {
  display: grid;
  grid-template-columns: repeat(4, var(--card-size));
  gap: 14px;
  justify-content: center;
  padding: 18px;
  background: linear-gradient(180deg, rgba(255,255,255,.04), transparent);
  border: 1px solid rgba(255,255,255,.06);
  box-shadow: var(--shadow);
  border-radius: var(--radius);
}

.card {
  width: var(--card-size);
  height: var(--card-size);
  perspective: 1000px;
  position: relative;
}
.card button {
  all: unset;
  cursor: pointer;
  width: 100%; height: 100%;
  display: block;
  position: relative;
  border-radius: 12px;
  outline-offset: 4px;
}
.card__inner {
  width: 100%; height: 100%;
  position: relative;
  transform-style: preserve-3d;
  transition: transform .5s ease;
}
.card[data-state="flipped"] .card__inner,
.card[data-state="matched"] .card__inner {
  transform: rotateY(180deg);
}

.card__face {
  position: absolute; inset: 0;
  backface-visibility: hidden;
  border-radius: 12px;
  display: grid; place-items: center;
  border: 2px solid rgba(255,255,255,.06);
  box-shadow: inset 0 0 0 1px rgba(255,255,255,.03), var(--shadow);
}

.card__face--back {
  background: linear-gradient(135deg, #1b2230, #12161e);
}
.card__face--front {
  transform: rotateY(180deg);
  background: linear-gradient(135deg, #0bf5, #0a8a);
  border-color: #00ffa6;
}

.card__icon {
  width: 60%;
  height: 60%;
  filter: drop-shadow(0 6px 12px rgba(0,0,0,.45));
}

.card:focus-within button { outline: 2px solid var(--accent); }

.btn {
  margin-top: 16px;
  padding: 10px 16px;
  border-radius: 10px;
  border: 0;
  font-weight: 700;
  box-shadow: var(--shadow);
}
.btn.primary { background: var(--accent-2); color: white; }
.btn.primary:hover { filter: brightness(1.05); }

.overlay {
  position: fixed; inset: 0; pointer-events: none; display: none; z-index: 10;
}

@media (max-width: 700px) {
  :root { --card-size: 80px; }
  .board { gap: 12px; }
}
@media (max-width: 480px) {
  :root { --card-size: 68px; }
  .board { grid-template-columns: repeat(3, var(--card-size)); }
}