intrinsic-ratio

@mixin instrinsic-ratio($width, $height, $position: relative)
{
    @if unit($width) != unit($height) {
        @warn "@include instrinsic-ratio-wrapper: $width and $height must share the same unit type, supplied was: #{$width} / #{$height}";
    }
    $w: to-unitless($width);
    $h: to-unitless($height);
    $ratio: $h / $w;
    $percent: $ratio * 100%;

    & {
        position: $position;
        height: 0;
        padding-bottom: $percent;
    }
}

@mixin maintain-aspect
{
    & {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
    }
}

@function to-unitless($val){
    @if unitless($val) {
        @return $val;
    }

    $u:unit($val);
    $u:if($u==px,1px,
       if($u==em,1em,
       if($u==rem,1rem,
       if($u=='%',1%,
       if($u==pt,1pt,
       if($u==pc,1pc,
       if($u==in,1in,
       if($u==mm,1mm,
       if($u==cm,1cm,
       1)))))))));

    @return $val/$u;
}