JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <div class="item">
        <span></span>
        <span></span>
        <span></span>
        <span></span>
    </div>
    <div class="item">
        <span></span>
    </div>
</div>

CSS

span {
    display: inline-block;
    width: 10px;
    height: 30px;
    border: 1px solid red;
}
.container {
    display: flex;
    display: -webkit-flex;
    border: 1px solid blue;
    width: 200px; 
    padding: 2px;

}
.item {
    flex-grow: 1;
    -webkit-flex-grow: 1;
    border: 1px solid green;
}