JSFiddle - React, Tailwind, and code Playground

HTML

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

CSS

.container {
    margin: 10px;
    border: 5px solid blue;
    height: 50px;
    display: table;
    table-layout: fixed;
    width: 300px;
}
.item {
    border: 3px solid red;
    height:100%;
    vertical-align:top;
    display: table-cell;
}
.item button{
    background:transparent;
    padding:0;
    margin:0;
    border:0;
    width:100%;
    height:100%;
}