Old IE support for SASS - OOCSS Boxes

OOCSS Boxes in SASS

$ie-support: 7 !default;

@mixin oobox($ie-corner-tag: false){ // can be any HTML tag including; div, b, span, etc.
	.box {
		.hd,.bd,.ft{
			@include clearfix-me(micro);
		}
		@if $ie-corner-tag { // this code only ever executes if you want rounded corners in IE<8. Better without.
			%corners-and-wrappers {
				display:block;
				background-repeat:no-repeat;
				font-size:1%; // make sure IE doesn't get "helpful" and inc the box size to = font-size
				position:relative;
				z-index:10;
			}
			%corner {
				@extend %corners-and-wrappers;
				height:10px; 
				width:10px;
			}
			%corner-right {
				float:right;
			}
			%corner-left {
				float:left;
			}
			%corner-top {
				overflow:hidden;
				margin-bottom:-32000px;// margin bottom needs to be < -9px 
			}
			%corner-bottom {
				margin-top:-10px;
			}
			.tl{background-position: left top;
				@extend %corner;
				@extend %corner-left;
				@extend %corner-top;
			}
			.tr{
				background-position: right top;
				@extend %corner;
				@extend %corner-right;
				@extend %corner-top;
			}
			.bl {
				background-position: left bottom;
				@extend %corner;
				@extend %corner-left;
				@extend %corner-bottom;
			}
			.br {background-position: right bottom;
				@extend %corner;
				@extend %corner-right;
				@extend %corner-bottom;
			}
			.top{
				background-position:center top;
				@extend %corners-and-wrappers;
			}
			.bottom{
				background-position:center bottom;
				_zoom:1; // zoom required for IE5.5 only
				@extend %corners-and-wrappers;
			}
		}
	}
	/* ----- simple (extends box) ----- */

	.simple{
		@extend .box;
		&> .inner {
			border:1px solid #D7D7D7;
			@include border-radius(7px);
		}
		if $ie-corner-tag {
			b {background-image:url(skin/simple_corners.png)\9;}
		}
	} 
}