sass: vertical centering

vCentering.scss

%vCentering {
  // https://css-tricks.com/centering-in-the-unknown/
  text-align: center;
  white-space: nowrap;
  overflow-x: hidden;
  &:before {
    content: "";
    display: inline-block;
    height: 100%;
    vertical-align: middle;
    margin-right: -.25em;
  }
}

%vCentering_inner {
  width: 100%;
  display: inline-block;
  vertical-align: middle;
}