JSFiddle - React, Tailwind, and code Playground

HTML

<div class="group">
  <div class="first">first</div>
  <div class="second">second</div>
</div>

CSS

.group {
  width: 100%;
}
.first,
.second {
  float: left;
  width: 100%;
}

@media (min-width: 1000px) {
  .first,
  .second {
    width: 50%;
  }
}




.first {
  background-color: #ddd;
}
.second {
  background-color: #eee;
}

JavaScript

var width = $(window).width();
    $( window ).resize(function() {
      if(width < 1000){ 
        $(".first").before($(".second"));
      }
    });