JSFiddle - React, Tailwind, and code Playground

HTML

<div class="outer">
    <div class="container">
        <button>Options</button>
        <ul>
            <li>Option 1</li>
            <li>Option Really Long Text</li>
            <li>Option 3</li>
        </ul>
    </div>
</div>

CSS

.outer {
    width: 500px;
}

.container {
    float: right;
    position: relative;
}

ul {
    position: absolute;
    right: 0;
}

ul li {
    border: 1px solid #dcdcdc;
}