.t228__maincontainer {
  transition: background-color 0.4s ease, box-shadow 0.4s ease;
}

.t228__maincontainer.t228__fixed {
  background-color: rgba(0,0,0,0.9); /* фон при скролле */
  box-shadow: 0 2px 8px rgba(0,0,0,0.3);
}