JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li><img src="https://img.buzzfeed.com/buzzfeed-static/static/enhanced/webdr03/2013/5/5/23/enhanced-buzz-11819-1367809268-11.jpg"></li>
  <li><img src="http://www.samerweddings.com/en/img/birthday/album/orginal/0.64044500%201391324553_cat-thumb%5B1%5D.jpg"></li>
  <li><img src="https://img.buzzfeed.com/buzzfeed-static/static/enhanced/webdr03/2013/5/5/23/enhanced-buzz-11819-1367809268-11.jpg"></li>
   <li><img src="https://img.buzzfeed.com/buzzfeed-static/static/enhanced/webdr03/2013/5/5/23/enhanced-buzz-11819-1367809268-11.jpg"></li>
  <li><img src="https://img.buzzfeed.com/buzzfeed-static/static/enhanced/webdr03/2013/5/5/23/enhanced-buzz-11819-1367809268-11.jpg"></li>
  <li><img src="https://img.buzzfeed.com/buzzfeed-static/static/enhanced/webdr03/2013/5/5/23/enhanced-buzz-11819-1367809268-11.jpg"></li>
</ul>

CSS

ul{
  list-style-type: none;
  margin: 0;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
}
li{
  width: 25%;
  display: flex;
}

img{
  flex:1 0  100%;
}