JSFiddle - React, Tailwind, and code Playground

HTML

<div id="ctrl">
    <input/>
    <div id="box"></div>
</div>

CSS

#ctrl
{
    width:130px; height:24px;
    position:relative;
    display:flex;
    overflow:hidden;
    box-sizing: border-box;
    border:solid 1px #CCC;
}
input
{
    box-sizing: border-box;
    background:#5ee;
    flex:1;
    min-width: 0;
}
#box
{
    box-sizing: border-box;
    width:40px; height:22px;
    background: linear-gradient(#eee 0%, #eee 40%, #CDCDCD 100%);
}