JSFiddle - React, Tailwind, and code Playground

HTML

<div id='container'>
	<div id='first-item'>first item</div>
	<div id='second-item'>second item</div>
</div>

CSS

#container {
    display: -webkit-box;
    display: -webkit-flex;
    display: -ms-flexbox;
    display: flex;
  }

  #first-item {
    max-width: 200px;
    -webkit-box-flex: 1;
    -webkit-flex: 1;
        -ms-flex: 1;
            flex: 1;
  }

  #second-item {
    margin-left: auto;
  }

  /* just some colors - not important */
  #container {
    height: 200px;
    width: 100%;
    background: red;
  }

  #container > div {
    background: blue;
  }