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;
    background-color: #ccc;
    height:30px;
    margin:0;
    padding:0;
    border:0;
}
.inner-one {
    width:30%;
    background-color: yellow;
    height:100%;
    margin:0;
    padding:0;
    border:0;
    display:inline-block;
}
.inner-two {
    width:70%;
    background-color: green;
    height:100%;
    margin:0;
    padding:0;
    border:0;
    display:inline-block;
}