@function px($value, $emBase: $mix-em-base, $remBase: $mix-rem-base) {
    @if unit($value) == 'em' {
        @return strip-unit($value) / $emBase * 1em;
    } @else if unit($value) == 'rem' {
        @return strip-unit($value) / $remBase * 1rem;
    } @else if unit($value) == 'px' {
        @return $value;
    } @else if unitless($value) {
        @if $value == 0 {
            @return 0;
        }
        @return $value * 1px;
    } @else {
        @error '$value parameter must be in EM, REM or PX';
    }
}