@mixin box-shadow($shadow...) {
    @if $enable-shadows {
        $result: ();

        @if (length($shadow) == 1) {
            // We can pass `@include box-shadow(none);`
            $result: $shadow;
        } @else {
            // Filter to avoid invalid properties for example `box-shadow: none, 1px 1px black;`
            @for $i from 1 through length($shadow) {
                @if nth($shadow, $i) != "none" {
                    $result: append($result, nth($shadow, $i), "comma");
                }
            }
        }
        @if (length($result) > 0) {
            box-shadow: $result;
        }
    }
}