public/sass/mixins/modal/modal.scss

@import "palette.scss";
@import "dimensions.scss";
@import "typography.scss";

@mixin modal {
  //position
  position: fixed;
  top: 0;
  left: 0;
  //dimensions
  width: 100%;
  height: 100%;
  //center children
  display: flex;
  justify-content: center;
  align-items: center;
  //hide it
  opacity: 0;
  pointer-events: none;
  transition: opacity .2s ease-in;
  &.open {
    opacity: 1;
    pointer-events: auto;
  }
  &:before {
    content: ' ';
    display: inline-block;
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.2);
  }
}