JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="content1">
        Dit is contentvlak 1
    </div>
    <div class="rightbar">
        dit is de rechterbalk!
    </div>
    <div class="content2">
        Dit is content 2
    </div>
</div>

CSS

.content1{
    width: 250px;
    height: 100px;
    background: green;
    float: left;
}

.rightbar{
    width: 250px;
    height: 200px;
    background: red;
    float: right;
}

.content2{
    width: 250px;
    height: 200px;
    float: left;
    background: yellow;
}
@media (max-width: 550px){
 .content1, .rightbar, .content2{
     float: none;
  }
}
#container{
    max-width: 500px; 
  border: 2px solid silver;
    overflow: hidden;

}