JSFiddle - React, Tailwind, and code Playground

HTML

<div id="slyFrame_parent">
a
</div>
<div id="slyScrollbar_parent">
b
</div>
<div id="slyScrollbar_child">
Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore era
</div>
<div id="slyFrame_child">
d
</div>

CSS

* {
    margin:0;
    padding:0;
}
div {
    height: 500px;
    float: left;
}
#slyFrame_parent {
    width: 60px;
    background-color: #bbb;
}
#slyScrollbar_parent {
    width: 16px;
    background-color: #ccc;
}
#slyScrollbar_child {
    background-color: #ddd;
    width: 20px;
}
#slyFrame_child {
    width: 16px;
    background-color: #eee;
}

JavaScript

function setWidth() {
    var a = 60,
        b = 16,
        c = document.getElementById('slyScrollbar_child'),
        d = 16,
        widthOfDivs = a + b + d,
        dW = window.innerWidth;
    c.style.width = dW - widthOfDivs + 'px';
}
setWidth();
window.onresize = setWidth;