Documentation with responsive theme (3.8+) will hide "not supported" banner behind navbar for mobile layouts

[epicfaace]

Ever since a responsive theme was introduced in for the 3.8+ docs (#46), one issue this theme has is that the banner "This document is for an old version of Python that is no longer supported" shows up incorrectly and behind the navbar for mobile layouts.

3.6 docs don't have this problem, since it's not using the responsive layout:

However, if I configure 3.8 docs to show this "not supported" warning, you can see the issue:

Note that this issue doesn't yet affect the docs -- it will only affect the docs once 3.8 is EOL on 2024-10-14 and the "not supported" warning is added. It does affect the efforts around deploy previews in python/cpython#92852, though, because deploy previews use the same code as the "not supported" warnings to show the "deployment preview" warnings.

This issue was originally mentioned in python/cpython#92852 (comment)