.contact-stack {
  position: fixed;
  right: var(--space-4);
  bottom: 160px;
  z-index: 40;
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.contact-stack__item {
  width: 52px;
  height: 52px;
  border-radius: var(--radius-full);
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-md);
  animation: contact-pulse 1.8s ease-in-out infinite;
}

.contact-stack__item--messenger {
  background: linear-gradient(135deg, #00c6ff, #0068ff, #a033ff, #ff5db1);
}

.contact-stack__item--zalo {
  background: #ffffff;
  border: 2px solid #0068ff;
}

.contact-stack__zalo-text {
  color: #0068ff;
  font-weight: 800;
  font-size: var(--text-md);
  font-style: italic;
}

.contact-stack__item--phone {
  background: var(--color-bg-white);
  border: 2px solid var(--color-accent-red);
}

@keyframes contact-pulse {
  0%, 100% { transform: scale(1); }
  50% { transform: scale(1.08); }
}

.back-to-top {
  position: fixed;
  right: var(--space-4);
  bottom: var(--space-6);
  z-index: 40;
  width: 44px;
  height: 44px;
  border-radius: var(--radius-full);
  background: var(--color-bg-white);
  color: var(--color-brand-blue);
  box-shadow: 0 0 0 1px rgba(0, 100, 189, 0.4);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition-base);
}

.back-to-top.is-visible {
  opacity: 1;
  pointer-events: auto;
}

@media (max-width: 600px) {
  .contact-stack {
    right: var(--space-2);
    bottom: 120px;
  }
  .contact-stack__item {
    width: 44px;
    height: 44px;
  }
}