$overlay: 'ui-overlay';

.#{$overlay} {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, .56);
  z-index: 1;
  visibility: hidden;
  opacity: 0; 
  &.#{$overlay}-visible {
    visibility: visible;
    opacity: 1;
  }
}