.backdrop {
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  position: absolute;
  display: block;
  z-index: 10;
  visibility: hidden;
}

.backdrop-transition {
  transition-duration: .2s;
  transition-timing-function: cubic-bezier(.25,.8,.25,1);
  transition-property: visibility;
}

.backdrop-dark {
  background-color: rgba(0,0,0,.8);
}