JSFiddle - React, Tailwind, and code Playground

HTML

<div id="row">
    <span class="col">COL1</span><!-- remove whitespace
 --><span class="col">COL2 Text added to this column so height is different</span><!-- remove whitespace
 --><span class="col">COL3</span><!-- remove whitespace
 --><span class="col">COL4</span><!-- remove whitespace
 --><span class="col">COL5</span><!-- remove whitespace
 --><span class="col">COL6</span>
</div>

CSS

#row {
    float:left;
    border:1px solid red;
}

.col { display:inline-block;vertical-align:top;
width:30%; border:1px solid black; margin:1%;}

@media screen and (max-width: 400px) {
    .col {width:45%;}
}