:root {
  --canvas-bg: radial-gradient(circle at 20% 20%, rgba(76, 201, 240, 0.25), transparent 60%),
                  radial-gradient(circle at 80% 30%, rgba(247, 37, 133, 0.16), transparent 65%),
                  #101521;
}

.intro-section {
  padding-top: 3rem;
}

.ballpit-section {
  padding: 3rem 0 4rem;
}

.ballpit-grid {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 1.5rem;
  align-items: stretch;
}

.canvas-card,
.control-card {
  background: rgba(18, 23, 36, 0.82);
  border: 1px solid rgba(76, 201, 240, 0.18);
  border-radius: 16px;
  padding: 1.6rem;
  box-shadow: 0 22px 40px rgba(0, 0, 0, 0.45);
  display: flex;
  flex-direction: column;
  gap: 1.4rem;
}

.canvas-card .card-header h2,
.control-card h2 {
  margin: 0 0 0.35rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--accent);
  font-size: 0.9rem;
}

.canvas-card .card-header p,
.control-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.6;
}

.canvas-frame {
  border-radius: 14px;
  border: 1px solid rgba(76, 201, 240, 0.2);
  background: var(--canvas-bg);
  padding: 1.2rem;
}

#ballCanvas {
  width: 100%;
  height: auto;
  display: block;
  background: transparent;
  border-radius: 12px;
  box-shadow: inset 0 18px 35px rgba(12, 16, 24, 0.6);
}

.control-grid {
  display: grid;
  gap: 0.75rem;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
}

.control-grid .btn {
  width: 100%;
  justify-content: center;
  font-weight: 600;
  letter-spacing: 0.03em;
}

.control-hint {
  font-size: 0.82rem;
  opacity: 0.85;
}

.tips-list {
  margin: 0;
  padding-left: 1.1rem;
  display: grid;
  gap: 0.4rem;
  color: var(--muted);
  font-size: 0.82rem;
}

.tips-list li::marker {
  color: var(--accent);
}

@media (max-width: 1024px) {
  .ballpit-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 640px) {
  .canvas-card,
  .control-card {
    padding: 1.25rem;
  }
  .control-grid {
    grid-template-columns: 1fr;
  }
}