JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outher">
    <div class="inner"></div>
</div>

CSS

.outher{
    
    width:200px;
    height:150px;
    background-color:#a00;
    border-radius:30px;
    overflow:hidden;
}
.inner{
    opacity:0.8;
    width:100%;
    height:100%;
    background-color:yellow;
}