@extend-able SASS placeholder selectors for filling position:relative'd containers.

SASS convenience placeholder selectors

%absolute {
  position: absolute;
}

%absolute-fill-width {
  @extend %absolute;
  left: 0;
  right: 0;
}

%absolute-fill-height {
  @extend %absolute;
  top: 0;
  bottom: 0;
}

%absolute-fill {
  @extend %absolute-fill-width;
  @extend %absolute-fill-height;
}