SASS - Div with background and flexible main area

gistfile1

$paddingHeight: 50px;
background: transparent url(../img/b2b-content-middle.png) repeat-y;
min-height: 400px;
padding: 30px 30px 0 30px;
margin-bottom: $paddingHeight;
position: relative;
.main-content {
  
  &:before,
  &:after {
    @include notext;
    content: ".";
    display: block;
    height: $paddingHeight;
    width: 711px;
    left: 0;
    position: absolute;
    background: red;
  }
  &:before {
    background: transparent url(../img/b2b-content-top.png) repeat-y;
    top: - $paddingHeight;
  }
  &:after {
    background: transparent url(../img/b2b-content-bottom.png) repeat-y;
    bottom: - $paddingHeight;
  }   
}