skillbox/client/src/styles/_visibility.scss

.hideable-element {
  position: relative;

  &--greyed-out {
    &::before {
      content: '';
      position: absolute;
      top: 0;
      left: 0;
      bottom: 0;
      right: 0;
      background: rgba(255, 255, 255, 0.5);
      z-index: 10;
    }
  }
}