By importing compass/layout in order to get more mixins and functions, one of them are Stretch which stretches the element to instead of writing a absolute position and top,right,bottom,left. without any arguments the function default values are 0.
@import "compass"; @import "compass/layout"; .bio { position: relative; &:after { background: rgba(black, 0.3); content: ""; position: absolute; @include stretch(10px, 5px, 10px, 5px); } }