JSFiddle - React, Tailwind, and code Playground

HTML

<div id="rectangle"></div>
<div id="circle"></div>
<div id="oval"></div>
<div id="triangle"></div>

CSS

div { margin: 10px; display: inline-block; }
#rectangle {
 width: 100px;
 height: 100px; 
 background: #ccc;        
}
#circle {
    width: 100px;
    height: 100px;
    border-radius: 50%;
    background: yellow;
}
#oval {
    width: 150px;
    height: 100px;
    border-radius: 50%;
    background: blue;
}
#triangle {
    width: 0;
    height: 0;
    border-left: 75px solid transparent;
    border-right: 75px solid transparent;
    border-bottom: 75px solid green;
}