JSFiddle - React, Tailwind, and code Playground

HTML

jagged edge on left<br/><br/>
<div class="tray">
    <div class="fill"></div>
</div>

CSS

.tray {
    height: 20px;
    background: #000;
    border-radius: 100px;
    height:30px;
    width:90%;
}
.fill {
    background:#eee;
    width:10%;
    height:100%;
    border-radius: 12px; /* still occurs without this! */
}