liquid.scss

$width-comp-size: 640px;

@function strip-unit($n) {
  @return $n / ($n * 0 + 1);
}

@function w($size) {
  $width: $size / $width-comp-size * 100%;

  @return $width;
}

@function m($size) {
  $margin: calc(100vw * #{strip-unit($size)} / #{strip-unit($width-comp-size)});

  @return $margin;
}

.foo {
  width: w(125px);
}

.bar {
  margin-bottom: m(20px);
}

.baz {
  width: w(40px);
  margin-bottom: m(270px);
}