Custom functions in Sass functions

[sandrojohanides]

See strip(), only seems to happen in native Sass functions (if()).

@function size($size, $base: $base-font-size, $unit: null) {
    @return if(
        $unit == 'px',
        strip($size) * strip($base),
        strip($size) / strip($base) + 0.00001
    );
}