JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

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

.col { float:left;
width:30%; border:1px solid black; margin:1%;}

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