JSFiddle - React, Tailwind, and code Playground

HTML

<div id="menubar">
    <div id="menu">
        <div class="button">
            <Button>Button 1</Button>
        </div>
        <div class="button">
            <Button>Button 2</Button>
        </div>
        <div class="button">
            <Button>Button 3</Button>
        </div>
        <div class="button">
            <Button>Button 4</Button>
        </div>
    </div>
</div>

CSS

#menubar {
    width: 100%;
    height: 100%;
    display: table;
    table-layout: fixed;
}
#menu {
    display: table-row;
}
#menu .button {
    position: relative;
    display: table-cell;
}
#menu .button Button {
    width: 100%;
}