Styling disclosure widgets

How can I add some (very) basic styles?

For starters, you might like to add a background color to your summary element, and then a border of the same color around the entirety of everything else. This ties the contents together, visually.

In order to get a border around the entirety of your non-summary content, put it all in a div (or some other containing element you deem appropriate):

<details>
  <summary>
    <h3>Here is your summary content</h3>
  </summary>
  <div>
    <p>We've put all our other content in a containing div.</p>
    <p>This way, we can put a border around (or otherwise style) this container.</p>
  </div>
</details>