SASS: mixin rem()

rem-mixin.scss

// Thanks to Maykel Loomans
// http://miekd.com/articles/sizing-type-leading-and-vertical-dimensions-with-rem-units/
$baseFontSize: 16px;
@mixin rem($property, $px_values) {
	$baseline_rem: ($baseFontSize / 1rem);
	#{$property}: $px_values;

	@if type-of($px_values) == 'number' {
		#{$property}: $px_values / $baseline_rem;
	} 
	@else {
		$rem_values: ();

		@each $value in $px_values {
			@if $value == 0 {
				$rem_values: append($rem_values, $value);
			} @else {
				$rem_values: append($rem_values, ($value / $baseline_rem) );
			}
		}
		#{$property}: $rem_values;
	}
}

rem-usage.scss

h1 {
	@include rem(font-size, 25px);
	@include rem(margin, 0 0 12px);
}

// Translates into:
h1 {
	font-size: 25px;
	font-size: 1.5625rem;
	margin: 0 0 12px;
	margin: 0 0 .75rem;
}

// Media Query to scale up/down the font size:
@media screen and (max-width: 600px) {
	html {
		font-size: 50%;
	}
}