JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outer">
    <div id="inner">
    </div>
</div>

CSS

#outer {
    width: 200px;
    background-color: white;
    border: 1px solid #ccc;
    -moz-border-radius: 10px;
    -webkit-border-radius: 10px;
    border-radius: 10px;
    overflow: hidden;
}

#inner {
    height: 100px;
    margin-top: 20px;
    background-color: #42749F;
    width: 200px;
    
    /* -1px here for to compansate for the outer border of the container */
    -moz-border-radius: 0 0 9px 9px;
}