Close bug report pop-up.

[s-moffatt]

• [ ] I have checked the latest main branch to see if this has already been fixed
• [ ] I have searched existing issues and pull requests for duplicates

URL to the section(s) of the book with this problem:

Description of the problem: It took me a few seconds to figure out how to close the bug report pop-up. It's not obvious that I need to click the bug icon again to close the pop-up box.

Suggested fix: Other websites I've seen allow the user to click anywhere outside of a pop-up to cancel it. Or have a close (X) button on the dialog itself.

[willcrichton]

Thanks for the report @s-moffatt. I will add a separate button to close the report window in the next mdbook-quiz release.