Create cross-browsing alpha transparent backgrounds.

RGBA-IE-backgroound.scss

// RGBa background
@mixin background-rgba($color, $alpha) {
  $rgba: rgba($color, $alpha);
  $ie-hex-str: ie-hex-str($rgba);
  // Fallback for web browsers that doesn't support RGBa
  background-color: $color;
  // Reset background to transparent only in IE 6-8 using the backslash 9 hack http://webdood.com/?p=57
  background-color: transparent\9;
  // RGBa with $alpha opacity
  background-color: $rgba;
  filter:progid:DXImageTransform.Microsoft.gradient(startColorstr=#{$ie-hex-str},endColorstr=#{$ie-hex-str});
  zoom: 1;
  	// Remove filter in IE9
	&:nth-child(n) {
		filter: none;
	}
}