example-seven.sass

%relative
  postion: relative
  
%padding--10
  padding: 10px

%margin-bottom--10 
  margin-bottom: 10px

%box 
  background: #f7f7f7
  color: black

%box_small 
  height: 200px
  width: 300px

%box_big 
  height: 400px
  width: 500px

.mybig--box
  @extend %box, %box_small, %padding--10
 
.mysmall--box
  @extend %box, %box_wide, %padding--10, %margin-bottom--10
  
.box--heading
  @extend %padding--10