JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="content"></div>
</div>

CSS

#container{
	position: relative;
	width: 100%;
}
#container:before{
	content: '';
	display: block;
	padding-top:100%;
}
#content{
	position:  absolute;
	top: 0;
	left: 0;
	bottom: 0;
	right: 0;
    background: 
        /* 1st row */
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 0 0 / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 33.3% 0 / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 66.6% 0 / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 100% 0 / 25%,
        
        /* 2nd row */
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 0 33.3% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 33.3% 33.3% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 66.6% 33.3% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 100% 33.3% / 25%,
        
        /* 3rd row */
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 0 66.6% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 33.3% 66.6% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 66.6% 66.6% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 100% 66.6% / 25%,
        
        /* 4th row */
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 0 100% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 33.3% 100% / 25%,
        url(http://upload.wikimedia.org/wikipedia/commons/3/3a/Kleurencirkel.svg) no-repeat 66.6% 100% / 25%,
       ...