JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="red">Red</div>
    <div class="green">green</div>
    <div class="blue">blue</div>
</div>

CSS

.container{border: 2px solid black; padding: 5px;  width: 100%;}

.container div {height: 20px; display: inline-block;}

.red{border: 2px solid red; width: 40px; float: left;}

.green{border: 2px solid green; width: 40px; float: left;}

.blue{border: 2px solid blue;
 width: calc(100% - 100px);
}