JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
    <div class="submain">
        <div class="anothersub">text</div>
    </div>
</div>

CSS

#main {
    width: 300px;
    background-color: red;
}
#main .submain {
    width: 66%;
    background-color: blue;
}
#main .submain .anothersub {
    width: 50%;
    background-color: yellow;
}