*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --bg: #1a1a1a;
  --fg: #fafafa;
  --card-bg: #2a2a2a;
  --card-border: rgba(255, 255, 255, 0.1);
  --muted: #a1a1a1;
  --ring: #555;
  --radius: 1rem;
}

body {
  font-family: "Segoe UI", system-ui, -apple-system, sans-serif;
  background: var(--bg);
  color: var(--fg);
  min-height: 100dvh;
  display: flex;
  flex-direction: column;
}

main {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  padding: 3rem 1rem;
}

header {
  text-align: center;
  margin-bottom: 2.5rem;
}

h1 {
  font-size: clamp(2rem, 5vw, 3rem);
  font-weight: 700;
  letter-spacing: -0.025em;
}

header p {
  margin-top: 0.75rem;
  font-size: 1.125rem;
  color: var(--muted);
  max-width: 28rem;
  margin-left: auto;
  margin-right: auto;
}

/* Grid */
.grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem;
  width: 100%;
  max-width: 40rem;
}

@media (min-width: 640px) {
  .grid {
    gap: 1.25rem;
  }
}

/* Card */
.card {
  perspective: 1000px;
  cursor: pointer;
  border-radius: var(--radius);
  outline: none;
}

.card:focus-visible {
  outline: 2px solid var(--ring);
  outline-offset: 2px;
}

.card-inner {
  position: relative;
  width: 100%;
  aspect-ratio: 1;
  transition: transform 0.6s ease-in-out;
  transform-style: preserve-3d;
}

.card.flipped .card-inner {
  transform: rotateY(180deg);
}

.card-front,
.card-back {
  position: absolute;
  inset: 0;
  border-radius: var(--radius);
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

/* Front */
.card-front {
  gap: 0.5rem;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  transition: transform 0.2s ease;
}

@media (min-width: 640px) {
  .card-front {
    gap: 0.75rem;
  }
}

.card:not(.flipped):hover .card-front {
  transform: scale(1.05);
}

.card:not(.flipped):active .card-front {
  transform: scale(0.95);
}

.card-front svg {
  width: 2rem;
  height: 2rem;
  filter: drop-shadow(0 2px 4px rgba(0, 0, 0, 0.2));
}

@media (min-width: 640px) {
  .card-front svg {
    width: 3rem;
    height: 3rem;
  }
}

.card-front span {
  font-size: 0.75rem;
  font-weight: 600;
  color: white;
  text-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
}

@media (min-width: 640px) {
  .card-front span {
    font-size: 1.125rem;
  }
}

/* Back */
.card-back {
  transform: rotateY(180deg);
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  padding: 0.75rem;
}

@media (min-width: 640px) {
  .card-back {
    padding: 1.5rem;
  }
}

.card-back p {
  text-align: center;
  font-size: 0.75rem;
  font-weight: 500;
  line-height: 1.6;
  color: var(--fg);
}

@media (min-width: 640px) {
  .card-back p {
    font-size: 1.125rem;
  }
}

/* Gradients */
.gradient-orange {
  background: linear-gradient(135deg, #f97316, #d97706);
}
.gradient-sky {
  background: linear-gradient(135deg, #0ea5e9, #2563eb);
}
.gradient-violet {
  background: linear-gradient(135deg, #8b5cf6, #9333ea);
}
.gradient-emerald {
  background: linear-gradient(135deg, #10b981, #16a34a);
}
.gradient-pink {
  background: linear-gradient(135deg, #ec4899, #e11d48);
}
.gradient-cyan {
  background: linear-gradient(135deg, #06b6d4, #0d9488);
}
.gradient-red {
  background: linear-gradient(135deg, #ef4444, #e11d48);
}
.gradient-yellow {
  background: linear-gradient(135deg, #eab308, #d97706);
}
.gradient-indigo {
  background: linear-gradient(135deg, #6366f1, #2563eb);
}

/* Reset Button */
.reset-btn {
  margin-top: 2rem;
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.75rem 1.5rem;
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--fg);
  background: transparent;
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  cursor: pointer;
  transition: background 0.15s ease;
}

.reset-btn:hover {
  background: rgba(255, 255, 255, 0.05);
}

.reset-btn:focus-visible {
  outline: 2px solid var(--ring);
  outline-offset: 2px;
}

.hidden {
  display: none !important;
}

/* Footer */
footer {
  text-align: center;
  padding: 1.5rem 1rem;
  font-size: 0.875rem;
  color: var(--muted);
}