Using rem with IE px fallback

_module.sass

// just use remify where appropriate
body
  margin: remify(32px 10px 0 24px)

ie.sass

// set output to px
$rem-to-px-conversion: true

@include "module"

screen.sass

@include "module"

the-mixin.scss

/**
 * BLOCK: convert rem to pixels for older browsers
 */

@function parseInt($n)
	@return $n / ($n * 0 + 1)

$rem-to-px-conversion: false !default
$rem-to-px-base: 16 !default

/**
 * converts pixel values to rem and provides a px fallback on a stylesheet base
 *
 * the sass variable $rem-to-px-conversion defaults to false.
 * for older browsers you can override this in a separate stylesheet and
 * all values will outputted as is without a conversion.
 *
 * the conversion base for px to rem conversions can be configuried
 * via $rem-to-px-base and defaults to 16 (as in most browsers)
 *
 * based on work by David Walsh: http://davidwalsh.name/rem-px-browser-function-sass
 *
 * @param  {String} $values One or more px values
 * @return {String} values in rem or px, depending on the configuration
 *
 * @example
 * margin: remify(32px 0 24px 0)
 * returns: margin: 2rem 0 1.5rem 0
 * and for IE: margin: 32px 0 24px 0
 */
@function remify($values)

	// sanity-checks
	@if not( global-variable-exists(rem-to-px-conversion) )
		@error 'Please provide variable named $rem-to-px-conversion'
	@if not( global-variable-exists(rem-to-px-base) )
		@error 'Please provide variable named $rem-to-px-base'

	$list: ()

	// there can be CSS attributes with more than one value
	@each $value in $values

		$unit : unit($value)
		$val  : parseInt($value)

		@if ($rem-to-px-conversion and $unit == 'px') // rem not supported / IE style
			$list: append($list, $value)

		@else if ($unit == 'px') // conversion to rem
			$list: append($list, ($val/$rem-to-px-base) * 1rem)

		@else if ($unit == 'em') // conversion to rem
			$list: append($list, $val * 1rem)

		@else if ($unit == 'rem')
			$list: append($list, $val)

		@else if ($unit == '') // unitless values, like in 'margin: 0 16px'
			$list: append($list, $value)

		@else
			@warn 'There is currently no unit conversion for #{$unit}'

	// do not return single value list - e.g. this makes math operations simpler
	@if length($list) == 1
		@return nth($list, 1)

	@return $list

/**
 * ENDBLOCK: convert rem to pixels for older browsers
 */