zdoc/assets/sass/components/_modal.scss

.modal {
  position: fixed;
  z-index: z('modal');
  left: -100%;
  top: 0;
  right: 0;
  bottom: 0;
  width: 100%; /* Full width */
  height: 100%; /* Full height */
  overflow: hidden;
  opacity: 0;
  background: rgba(0,0,0,0.6);

  @include transition(opacity, 0.25s, ease-in-out);
}