Banner is off-center on larger screen sizes

What version of starlight are you using?

0.21.5

What version of astro are you using?

4.6.0

What package manager are you using?

pnpm

What operating system are you using?

Mac, but happens on any OS

What browser are you using?

Chrome, but happens on any browser

Describe the Bug

The banner is not centered correctly on larger screens.

On smaller screens, the banner is aligned with the center of the page and the content. I'd expect that to remain true as the screen-size increases. However, once the content reaches its maximum width, the banner gets off-center since it is actually being centered on the total space between the two sidebars.

Link to Minimal Reproducible Example

https://stackblitz.com/edit/github-alovcj?file=src%2Fcontent%2Fdocs%2Findex.mdx

Participation

• I am willing to submit a pull request for this issue.