JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="box red">1 red (height 50px)</div>
    <div class="box yellow flexible">2 yellow (flexible height)</div>
    <div class="box green">3 green (height 50px)</div>
 </div>

CSS

.container {
    width: 200px;
    height: 200px;
    background: #999;
    border: 1px solid #000;
    
    display: -webkit-flex;
    display: -moz-flex;
    display: flex;
    flex-flow: column;
}
    
.box {
    -webkit-flex: none;
    flex: none;
    width: 200px;
}

.box.flexible {
    flex: 1 1 auto;
}

.box.red {
    background: red;
}

.box.yellow {
    background: yellow;
}

.box.green {
    background: green;
}