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

html, body {
  width: 100%;
  min-height: 100vh;
  background: #1a1a1a;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}

.overlay {
  position: fixed;
  top: 0; left: 0;
  width: 100%; height: 100%;
  background: rgba(0, 0, 0, 0.85);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 999;
  transition: opacity 0.5s ease;
}

.overlay.hidden { opacity: 0; pointer-events: none; }

.overlay-content { text-align: center; }

.start-btn {
  padding: 18px 60px;
  font-size: 22px;
  font-weight: 600;
  color: #fff;
  background: linear-gradient(135deg, #667eea, #764ba2);
  border: none;
  border-radius: 50px;
  cursor: pointer;
  letter-spacing: 2px;
  box-shadow: 0 4px 20px rgba(102, 126, 234, 0.4);
  transition: transform 0.2s, box-shadow 0.2s;
  -webkit-tap-highlight-color: transparent;
}

.start-btn:hover { transform: scale(1.05); box-shadow: 0 6px 30px rgba(102, 126, 234, 0.6); }
.start-btn:active { transform: scale(0.97); }

.video-grid {
  position: relative;
  display: grid;
  grid-template-columns: 1fr 1fr;
  grid-template-rows: 1fr 1fr 1fr;
  gap: 6px;
  width: 100%;
  max-width: 720px;
  aspect-ratio: 2 / 3;
  padding: 6px;
}

.cell {
  position: relative;
  width: 100%; height: 100%;
  background: #000;
  border-radius: 4px;
  overflow: hidden;
}

.thumb {
  width: 100%; height: 100%;
  object-fit: cover;
  display: block;
  background: #000;
}

.cell.playing .thumb { visibility: hidden; }

.cell.playing { box-shadow: inset 0 0 0 3px #667eea, inset 0 0 20px rgba(102, 126, 234, 0.5); }

.video-player {
  position: absolute;
  z-index: 3;
  display: none;
  object-fit: contain;
  background: #000;
  border-radius: 4px;
  cursor: pointer;
  box-shadow: 0 0 0 3px #667eea, 0 0 20px rgba(102, 126, 234, 0.5);
}

@media (max-width: 480px) {
  .video-grid { gap: 4px; padding: 4px; }
  .start-btn { padding: 14px 40px; font-size: 18px; }
}

@media (min-width: 1024px) {
  .video-grid { max-width: 900px; }
}