JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.main {
    background-color: yellow;
    width: 400px;
    height: 40px;
    position: relative;
}
.main div {
    position: absolute;
    top: 40px;
    border: 7px solid white;
    border-top: 7px solid grey;
    border-right: 7px solid grey;
}