:root {
  --bg: #0b0f14;
  --card: #131a22;
  --card-border: #243142;
  --text: #e8eef6;
  --muted: #90a3b3;
  --accent: #6aa9ff;
}
* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: Inter, system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  color: var(--text);
  background: radial-gradient(1200px 800px at 20% -10%, #132136 0, #0b0f14 60%);
}
.site-header { padding: 24px 20px 8px; text-align: center; }
.site-header h1 { margin: 0 0 6px; font-size: 28px; letter-spacing: .2px; }
.site-header p { margin: 0; color: var(--muted); }
.controls { display: flex; gap: 10px; padding: 14px 20px; justify-content: center; flex-wrap: wrap; }
.controls input[type="search"] {
  min-width: 260px; padding: 10px 12px; border-radius: 10px; border: 1px solid var(--card-border); background: var(--card); color: var(--text);
}
.controls button { padding: 10px 14px; border: 1px solid var(--card-border); background: #182232; color: var(--text); border-radius: 10px; cursor: pointer; }
.controls button:hover { border-color: var(--accent); }
.grid {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(260px, 1fr)); gap: 16px; padding: 16px 20px 60px;
}
.card {
  perspective: 1200px; height: 200px;
}
.card-inner {
  position: relative; width: 100%; height: 100%; transform-style: preserve-3d; transition: transform .5s ease;
}
.card.flipped .card-inner { transform: rotateY(180deg); }
.card-face {
  position: absolute; inset: 0; border-radius: 14px; border: 1px solid var(--card-border); background: linear-gradient(180deg, #121a24, #0f151d);
  padding: 14px; display: flex; align-items: center; justify-content: center; text-align: center; backface-visibility: hidden;
}
.card-face.back { transform: rotateY(180deg); }
.term { font-weight: 700; font-size: 18px; letter-spacing: .2px; }
.definition { font-size: 14px; color: var(--muted); line-height: 1.45; }
.site-footer { text-align: center; color: var(--muted); padding: 28px 0; border-top: 1px solid #122032; background: #0b0f14; }