JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
<div class="first-div">first div </div>
<div class="second-div">second div </div>
</div>

CSS

.first-div{
   -webkit-flex: 1; /* Safari 6.1+ */
   flex: 1;
    background-color:yellow;
   border: 2px solid black; 
}

.second-div{
    -webkit-flex: 1; /* Safari 6.1+ */
   flex: 1;
    background-color:blue;
     border: 2px solid black;  
}
.container{
    width:auto; 
    display: -webkit-flex; /* Safari */
    -webkit-align-items: center; /* Safari 7.0+ */
    display: flex;
    align-items: center;
}