<===> input.scss
foo {
    filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="data:image/png;base64,ABCD",sizingMethod=crop);
}

<===> output.css
foo {
  filter: progid:DXImageTransform.Microsoft.AlphaImageLoader(src="data:image/png;base64,ABCD",sizingMethod=crop);
}