:root {
  --rocket-size: 52px;
  --rocket-bg: linear-gradient(135deg, #0ea5e9 0%, #7c3aed 100%);
  --rocket-shadow: 0 10px 25px rgba(124, 58, 237, 0.35);
  --rocket-glow: 0 0 25px rgba(124, 58, 237, 0.6);
  --accent: #ffffff;
  --rocket-offset-bottom: 120px;
}

.rocket-btn {
  position: fixed;
  bottom: var(--rocket-offset-bottom);
  right: 24px;
  z-index: 999;
  width: var(--rocket-size);
  height: var(--rocket-size);
  background: var(--rocket-bg);
  color: var(--accent);
  border-radius: 50%;
  font-size: 22px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  transition: opacity 0.3s ease, transform 0.3s ease, box-shadow 0.3s ease;
  opacity: 0;
  transform: scale(0.8);
  pointer-events: none;
}

.rocket-btn i {
  transform: rotate(-18deg);
}

.rocket-btn.show {
  opacity: 1;
  transform: translateY(0) scale(1);
  pointer-events: auto;
}

.rocket-btn:hover {
  box-shadow: var(--rocket-shadow), var(--rocket-glow);
  filter: brightness(1.1);
  transform: translateY(-3px) scale(1.05);
}

.rocket-btn:active {
  transform: translateY(0) scale(0.95);
}

.rocket-btn::after {
  content: "";
  position: absolute;
  bottom: -10px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: radial-gradient(circle at 30% 30%, #ffdd55, #ff6b6b 60%, transparent 70%);
  opacity: 0;
  transform: translateY(6px);
  transition: opacity 200ms ease, transform 200ms ease;
}

.rocket-btn:hover::after {
  opacity: 0.9;
  transform: translateY(0);
}


/* Dark mode thân thiện (tuỳ chọn) */
@media (prefers-color-scheme: dark) {
  :root {
    --rocket-shadow: 0 10px 25px rgba(124, 58, 237, 0.45);
    --rocket-glow: 0 0 28px rgba(124, 58, 237, 0.8);
  }
}

/* Tránh che footer trên mobile */
@media (max-width: 480px) {
  .rocket-btn {
    right: 16px;
    bottom: 16px;
    width: 46px;
    height: 46px;
  }
  .rocket-btn i {
    font-size: 20px;
  }
}