.scroll-to-top {
  position: fixed;
  bottom: 1.25rem;
  right: 1.25rem;
  z-index: 999;
  display: flex;
  height: 2.75rem;
  width: 2.75rem;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  border: 1.5px solid #d1d5db;          /* border xám nhạt */
  border-radius: 0.75rem;
  background-color: #f8fafc;            /* nền rất nhạt */
  color: #64748b;                       /* icon xám nhẹ */
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.06);
  transition: all 0.25s ease;
}

.scroll-to-top:hover {
  transform: translateY(-0.25rem);
  background-color: #e2e8f0;            /* hover nền đậm hơn một chút */
  border-color: #94a3b8;
  color: #475569;
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.1);
}

.scroll-to-top:active {
  transform: scale(0.95);
}

/* Responsive */
@media (min-width: 640px) {
  .scroll-to-top {
    bottom: 1.5rem;
    right: 1.5rem;
    height: 3rem;
    width: 3rem;
  }
}