JSFiddle - React, Tailwind, and code Playground

HTML

<div id="wrapper">
    <div id="content">
        <img src="http://farm3.staticflickr.com/2783/4106818782_cc6610db2c.jpg">        
    </div>
</div>
<br>
Resize the window and see. Always stays 3:1

CSS

#wrapper {
    position: relative;
    padding-bottom: 33.33%; /* Set ratio here */
    height: 0;
}
#content {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: green;
    text-align: center;
}
#content img {
    max-height: 100%;
}