JSFiddle - React, Tailwind, and code Playground

HTML

<div class="colwrap">
  <div class="red">

  </div>
  <div class="blue">

  </div>
</div>

CSS

.colwrap {
  display:flex;
  flex-wrap:wrap;
}

.red,
.blue {
  flex:0 0 400px;
}

.red {
  background-color: red;
  height: 400px;  
}

.blue {
  background-color: blue;
  height: 2000px;
}

@media screen and (min-width: 900px) {
  .red {
    order:2;
  }
  
  .blue {
    order:1;
  }
}