Simple Sass mixin for responsive css: start height / width / margin / font-size/etc. at one size, and shrink when the screen is smaller.

responsive-measure.scss

/*
 * Set a measure to a standard size on large screens,
 * and beneath 750 pixels width, scale it according to screen width.
 * Useful for margins, padding, font-sizes: anything which takes a measure.
 * Works with absolute measures (px, pt, etc., also rem), not
 * with relative measures (em, etc.)
 *
 * Usage:
 * foo {
 *     @include responsive-measure(margin,20px);
 * }
 */
@mixin responsive-measure($measure,$basis) {
	#{$measure}: $basis;
	@media (max-width: 749px) {
		$unitless: $basis / (0 * $basis + 1);
		#{$measure}: $unitless * 0.1333vw;
	}
}