JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer-box">
    <div class="inner-one"></div>
    <div class="inner-two"></div>
</div>

CSS

.outer-box {
    width:200px;
    display:table;
    border-collapse:collapse;
}
.inner-one, .inner-two {
    display:table-cell;
    background:green;
}
.inner-one {
    width:30%;
    background:yellow;
    height:1.2em; /* in case tested with no content */
}