/* ===== N-BACK CHALLENGE ===== */
.nb-stage {
  width: 100%;
  max-width: 400px;
  height: 220px;
  background: var(--card);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border: 1px solid var(--card-border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  position: relative;
}
.nb-shape {
  font-size: 6rem;
  text-shadow: 0 8px 24px rgba(0,0,0,0.5);
}
.nb-shape.pop {
  animation: popShape 0.3s cubic-bezier(0.175,0.885,0.32,1.275);
}
@keyframes popShape {
  0% { transform: scale(0.5); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}
.nb-message {
  position: absolute;
  top: 16px;
  color: #fff;
  font-size: 1rem;
  font-weight: 800;
  text-shadow: 0 2px 8px rgba(139, 92, 246, 0.8);
  letter-spacing: 1px;
}
.nb-actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  width: 100%;
  max-width: 400px;
  transition: opacity 0.3s;
}
.nb-actions .btn-outline {
  padding: 16px;
  font-size: 1.25rem;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  background: rgba(255,255,255,0.05);
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}
.nb-actions .btn-outline:active {
  transform: scale(0.95);
}