JSFiddle - React, Tailwind, and code Playground

HTML

<div class="box b1"></div>
<div class="box b2"></div>
<div class="box b3"></div>
<div class="box b4"></div>

CSS

.box {
    width:200px;
    height:200px;
    margin:20px;
    float:left;
    
}
.b1 {
    border: 4px double #ff0000;
    border-radius: 200px;
}
.b2 {
    border: 4px solid #0000ff;
    border-radius: 20px;
}
.b3 {
    border: 4px solid #000000;
    border-radius: 20px 50px 10px 4px;
}
.b4 {
    border: 4px solid #000000;
    border-radius: 50px/20px 40px 10px 4px;
}