JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="a">a</div>
    <div class="b">b</div>
</div>

CSS

.main{
    padding: 1em;
}
.a{
    background-color:#ccc;
    padding: 1em;
    float: left;
    box-shadow: 0px 0px 1.5em #dadbdd;
}
.b{
    clear: both;
    background-color:#ccc;
    padding: 1em;
    box-shadow: 0px 0px 1.5em #dadbdd;
}