JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="inner1"></div>
</div>
<div id="afterfloat"></div>

CSS

#container{
    float:left;
    background: grey;
    border: 1px solid black;
}

#inner1{
    float: left;
    width: 100px;
    height: 100px;
    background: red;
    border: 1px solid black;
}

#container:after{
   content: "."; 
   visibility: hidden; 
   display: block; 
   height: 0; 
   clear: both;
}

#afterfloat{
    float: left;
    width: 100px;
    height: 100px;
    background: green;
    border: 1px solid black;
}