JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="left">fixed width</div>
    <div id="right">rest of space width</div>
</div>

CSS

#container {
float:left;
width:100%;
}
#left, #right {
    padding:50px;
    background: #ccc;
    vertical-align: bottom;
    display: inline-block;
    /* ie6/7 */
    *display: inline;
    zoom: 1;
}


#right {
padding:20px;
background:#000;
color:#fff;
}