SCSS mixin for REMs (done with jondaiello)

_mixins.scss

@mixin rem-width( $em-size ) {
  width: $em-size * $base-font-multiplier * 16px;
  width: $em-size * 1rem;
}

_smallest.scss

html {
  font-size: $base-font-size;
}

_variables.scss

$base-font-multiplier: 1; // master font size integer
$base-font-size: $base-font-multiplier * 100%;