JSFiddle - React, Tailwind, and code Playground

HTML

<div id="outerDiv">
    <div id="innerDiv"></div>
    <div id="remainderDiv"></div>
</div>

CSS

#outerDiv, #innerDiv, #remainderDiv{
    height: 100px;
}
#outerDiv{
    width: 55.5px;
    z-index: 1;
    background-color: red;
}
#innerDiv{
    width: calc(100% - 10px);
    z-index: 100;
    background-color: blue;
    float: left;
}
#remainderDiv{
    width: 10px;
    z-index: 100;
    background-color: green;
    float: left;
}