/* Scroll-to-top button — в палитре сайта (тёмный фон + красный акцент #E50914) */
.stt-btn {
  position: fixed;
  right: 24px;
  bottom: 100px;
  width: 56px;
  height: 56px;
  border-radius: 50%;
  background: #1a1a1a;
  border: 2px solid #E50914;
  color: #E50914;
  cursor: pointer;
  display: grid;
  place-items: center;
  padding: 0;
  opacity: 0;
  visibility: hidden;
  transform: translateY(20px);
  transition: opacity 0.3s ease, visibility 0.3s ease, transform 0.3s ease, background 0.25s ease, box-shadow 0.25s ease, color 0.25s ease;
  box-shadow: 0 4px 16px rgba(229, 9, 20, 0.25);
  z-index: 2147483000;
}
.stt-btn.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}
.stt-btn:hover {
  background: #E50914;
  color: #fff;
  transform: translateY(-3px);
  box-shadow: 0 6px 22px rgba(229, 9, 20, 0.45);
}
.stt-btn:active {
  transform: translateY(-1px);
}
.stt-btn svg {
  width: 24px;
  height: 24px;
  display: block;
}
@media (max-width: 640px) {
  .stt-btn { right: 16px; bottom: 88px; width: 48px; height: 48px; }
  .stt-btn svg { width: 20px; height: 20px; }
}
@media (prefers-reduced-motion: reduce) {
  .stt-btn { transition: opacity 0.2s ease; }
}