JSFiddle - React, Tailwind, and code Playground

by Sub Lines

HTML

<div class=page>
    <div id=main>Foo</div>
    <div id=side>Bar</div>
</div>

CSS

* {
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box;
}

.page {
    display: -webkit-flex;
    display: -moz-flex;
    display: flex;
}
.page > div {
    padding: 20px;
    -webkit-flex: 1;
    -moz-flex: 1;
    flex: 1;
}

#main {
    background: #bbb;
}
#side {
    background: #ddd;
    -webkit-flex: 0 0 200px;
    -moz-flex: 0 0 200px;
    flex: 0 0 200px;
}