JSFiddle - React, Tailwind, and code Playground

HTML

<div><img src='http://domsovkusom.com/img/products/textile/blind_room/SDC17335.jpg'></div>

CSS

html {
    font-size:16px;    
}

div {
    width: 20em;
    height: 20em;
    border: 1px solid red;
}

img {
border: 1px solid green;
  width: 50%; /* width: 0.5em */
  height: 50%; /* height: 0.5em */
}