JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
    <li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
    <li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
<li><img src="http://img.dummy-image-generator.com/abstract/dummy-40x40-Utrecht.jpg" /></li>
</ul>

CSS

li
{
    float:left;
    width:50px;
}
li:nth-child(6n+1)
{
    clear:both;
}

li:nth-child(2n) img
{
    border:solid 2px red;
}