JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div class="item">Foo</div>
    <div class="item">Bar</div>
</div>

CSS

#container {
    background-color: green;
    display: flex;
    overflow: auto;
}
.item {
    background-color: white;
    border: 1px solid black;
    flex-grow: 1;
    min-width: 200px;
    max-width: 300px;
}

.item:first-child {
    margin-left: auto;
}
.item:last-child {
    margin-right:auto;
}