JSFiddle - React, Tailwind, and code Playground

HTML

16px
<div>
    32px
    <p>
        32px
        <span>16px</span>
    </p>
</div>

CSS

body {
    font-size: 1em; /* 16px */
}

div {
    font-size: 2em; /* 32px */
}

p {
    font-size: 1em; /* 32px */
}

span {
    font-size: 0.5em; /* 16px */
}