GitHub style dropdowns formatting incorrectly

[brandonsturgeon]

Describe the bug GitHub style dropdowns display incorrectly in the Preview, regardless of zoom level.

Example of a dropdown:

<details open>
<summary>Want to ruin the surprise?</summary>
<br>
Well, you asked for it!
</details>

How it looks in GitHub:

How it looks in the preview:

Desktop (please complete the following information):

• OS: Linux, WSL2, viewing the preview on Windows using the latest Firefox (issue is present in Chrome also)