Rem Fallback

_rem-fallback.scss

/* Set up a variable for maths */

$doc-font-size: 16;

/* the font-size mixin */

@mixin font-size($size) {
  font-size: 0px + $size;
  font-size: 0rem + $size / $doc-font-size;
}

/* example of usage */

.prose p {
  @include font-size(16);  
}

/* example compiled */

.prose p {
  font-size: 16px;
  font-size: 1rem;
}