JSFiddle - React, Tailwind, and code Playground

HTML

<div class="lhs">
    <header>Header</header>
    <div class="panel-container">
        <ul>
            <li>Item 1</li>
            <li>Item 2</li>
            <li>Item 3</li>
            <li>Item 4</li>
            <li>Item 5</li>
        </ul>
    </div>
</div>

CSS

.lhs {
    position: absolute;
    top: 8px;
    left: 8px;
    width: 250px;
    height: 100px;
    border: 1px solid red;
    
    display: flex;
    flex-direction: column;
}

.panel-container {
    flex: 1;
    overflow: auto;
}