@function em($val, $base: $base) {
    @return $val / $base +em;
}
@function px($val) {
    @return $val +px;
}
@function pc($val) {
    @return #{$val +'%'};
}
@function nil($val) {
    @return $val;
}
@function vp($val, $suf) {
    @return $val + v#{$suf};
}