No, it will not override the CSS (not sure what you mean by "accessibility enabled" exactly).

> even with the focus outline disabled on other sites, I am able to navigate with the keyboard to text input fields

Correct, but for a user with vision problems, the focus outline lets them see what has focus. CSS doesn't stop them from inputting values.

Focus styles are essential and should not be removed as a best practice (in general, this is a very small site).

You are making the assumption that the user has some modicum of control over the browser's configuration.

No I am not. Users who require accessibility have it setup in their MacOS/Windows settings. It's a global setting for them. It's not website specific.

Users may access the site through a third-party device that they cannot configure, for example in a kiosk setting.

I mean we are talking about a demo project on hosting a tiny site on a calculator. Don't think anyone is trying to access it from a kiosk.

But if your comment is a general opinion of websites in general, then yea, I see what you mean.