PUG
.auth
  .auth_block

 SCSS
.auth {
  background: grey;
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  text-align: center;
  &:before {
    content:"";
    display: inline-block;
    height: 100%;
    width: 0;
    vertical-align: middle;
  }
}
.auth_block {
  width: 200px;
  height: 200px;
  background: yellow;
  display: inline-block;
  vertical-align: middle;
}