Javascript - 选择元素子元素的第一个元素

I have the following HTML:

我有以下HTML:

<div class="list">
<div class="items">
    <ul>
        <li>IMPORTANT</li>
        <li>...</li>
        <li>...</li>
        <li>...</li>
        <li>...</li>
        <li>...</li>
    </ul>
    <ul>
        ...
    </ul>
</div>
<div c