:root {
  --bg-1: #0a1828;
  --bg-2: #1b263b;
  --panel: #e9f1f7;
  --ink: #11212d;
  --accent: #d97706;
  --accent-2: #0f766e;
  --warn: #b91c1c;
  --muted: #475569;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Trebuchet MS", "Segoe UI", sans-serif;
  color: var(--ink);
  background: radial-gradient(circle at 15% 10%, #264653 0%, transparent 40%),
    radial-gradient(circle at 85% 80%, #2a9d8f 0%, transparent 32%),
    linear-gradient(135deg, var(--bg-1), var(--bg-2));
}

.app {
  width: min(980px, 94vw);
  margin: 24px auto;
  background: color-mix(in srgb, var(--panel) 88%, white 12%);
  border-radius: 14px;
  padding: 20px;
  box-shadow: 0 10px 30px rgb(0 0 0 / 0.28);
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 14px;
}

.topbar h1 {
  margin: 0;
  font-size: clamp(1.3rem, 1.6vw + 1rem, 2rem);
}

.topbar-actions,
.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.stats {
  display: flex;
  gap: 18px;
  flex-wrap: wrap;
  margin: 10px 0 14px;
  font-weight: 600;
}

.flashcard {
  border: 2px solid #c5d3dc;
  border-radius: 12px;
  overflow: hidden;
  min-height: 330px;
  background: #fff;
}

.side { padding: 14px; }
.hidden { display: none; }

.video-wrap {
  position: relative;
  width: 100%;
  aspect-ratio: 16 / 9;
  border-radius: 10px;
  overflow: hidden;
  background: #0f172a;
}

video {
  width: 100%;
  height: 100%;
  border: 0;
  display: block;
}

#techniqueName { margin: 0; font-size: clamp(1.2rem, 1.2vw + 1rem, 2rem); }
.controls { margin-top: 12px; }

button {
  border: 0;
  border-radius: 9px;
  padding: 10px 12px;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  color: #fff;
  background: var(--accent-2);
}

button:hover { filter: brightness(1.07); }
button:disabled { opacity: 0.55; cursor: not-allowed; filter: none; }

#unknownBtn { background: var(--warn); }
#flipBtn, #shuffleBtn { background: var(--accent); }
#maskTextBtn, #repeatUnknownBtn { background: var(--muted); }

.video-wrap.mask-bottom video {
  transform: scale(1.08) translateY(-5%);
  transform-origin: center;
}

.video-wrap.mask-bottom::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 20%;
  background: #0f172a;
  pointer-events: none;
}

@media (max-width: 700px) {
  .app { padding: 14px; margin: 12px auto; }
}