JSFiddle - React, Tailwind, and code Playground

HTML

<p>foo bar</p>

SCSS

@function -em($wanted, $inherited) {
  @return ($wanted / $inherited) + 'em';
}

@function -pc($wanted, $parent) {
  @return (($wanted / $parent) * 100) + '%';
}

p {
    font-size: -em(40,16);
}