JSFiddle - React, Tailwind, and code Playground

HTML

<div class="menu">
    <div id="side">
        <ul>
            <li>Item1</li>
            <li>Item2</li>
            <li>Item3</li>
        </ul>
    </div>
</div>

CSS

.menu {
    right: 0;
    position: absolute;
    top: 243px;
    width: 250px;
    z-index: 5;
}

#side {
    background: #ace;
    position:fixed;
    width: 250px;
}

JavaScript

$(window).scroll(function(){
        $("#side").css("top",Math.max(15,243-$(this).scrollTop()));
    });