JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <ul>
        <li>
            <ul>
                <li><label>wtf</label></li>  
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li> 
                <li><label>wtf</label></li>            
            </ul>                    
        </li>
        <li>HEY!</li>
    </ul>
</div>

CSS

div {
    overflow: hidden;
    width: 100px;
    height: 100px;
}

div > ul {
    height: 100px;
    width: 200px;
}

div > ul > li {
    float: left;
    width: 100px;
    height: 100px;
    border: 1px solid red;
    box-sizing: border-box;
}

div > ul > li > ul {
    overflow-y: scroll;
    height: 50px;
    width: 100px;
}