body,html { margin:0; height:100%; }
#bgvid { position:fixed; right:0; bottom:0; min-width:100%; min-height:100%; object-fit:cover; }
.overlay {
  position:fixed; inset:0; display:flex; flex-direction:column;
  align-items:center; justify-content:center; color:#fff; text-shadow:0 2px 8px rgba(0,0,0,.7);
}
.overlay button {
  margin-top: 16px; padding: 10px 20px; border:0; border-radius:8px; cursor:pointer; font-weight:600;
}