$psdSize: 750px;
$refer: 750px;
@function px2rem($px, $psdSize: $psdSize, $refer: $refer) {
    @return $refer / $psdSize * $px / 100 * 1rem;
}
@function pr($px, $psdSize: $psdSize, $refer: $refer) {
    @return px2rem($px, $psdSize, $refer)
}