JSFiddle - React, Tailwind, and code Playground

HTML

Resize this window until the divs switch places.
<div class="wrapper">
    <div id="first_div" class="col">first div</div>
    <div id="second_div" class="col">second div</div>
</div>

CSS

.wrapper {
    display: flex;
    flex-direction: row;
}
.col {
    width: 100px;
    float: left;
    border: 1px solid black;
    padding: 5px;
    /*flex-grow: 1;*/
}
#first_div {
    background: yellow;
    height: 200px;
}
#second_div {
    background: cyan;
    height: 100px;
}
@media (max-width: 400px) {
    .wrapper {
        flex-direction: row-reverse;
        justify-content: flex-end;
    }
}