Create a file called test.html with the following content:

<style>
  body {
    background: #ffffff99;
  }
</style>

This is a rendering bug.

In Ladybird, navigate to a page (e.g. en.wikipedia.org). Once it loads, navigate to test.html. Due to the transparent background, Ladybird draws the new page on top of the previous page, causing the two pages to visually overlap. I see this behavior whether I run Ladybird on an M1 Macbook Air, or whether I use the Browser in Serenity:

For comparison, Chrome erases any sign of the previous page: