JSFiddle - React, Tailwind, and code Playground

HTML

<div id="base">
    50px
    <div class="em05">
        0.5em = 25px;
    </div>
    <div class="em2">
        2em = 100px
        <div class="em05">
            0.5em = 50px
        </div>
    </div>
</div>

CSS

#base{
    font-size:50px;
}
.em05{
    font-size:0.5em;
}
.em2{
    font-size:2em;
}
div{
    border:1px solid black;
    padding:10px;
}