JSFiddle - React, Tailwind, and code Playground

HTML

<div class="overflow">
    <div class="wrapper">
        <div class="content">
            Foobar
        </div>
    </div>
</div>

CSS

.overflow {
    width: 400px;
    overflow-y: auto;
    border: 1px solid black;
}

.wrapper {
    border: solid 15px white;
}

.content {    
    width: 800px;
    background: red;
    position: relative;
}

.content::after {
    content: '\a0';
    position: absolute;
    top: 0;
    right: -15px;
}