JSFiddle - React, Tailwind, and code Playground

HTML

<div id="div1">20% 5%<br>Chrome Dev: 20% 5%</div>    
<div id="div2">20% / 10%<br>Chrome Dev: 20% 5%</div> 
<div id="div3">20% \/ 5%<br>Chrome Dev: 20% 5%</div>

CSS

div {
    background: red;
    width: 100px;
    height: 100px;
    margin: 20px;
    text-align: center;
    line-height: 33px;
}

JavaScript

$('#div1').css({'border-radius': '20% 5%'});
$('#div2').css({'border-radius': '20% / 10%'});
$('#div3').css({'border-radius': '20% \/ 5%'});