Markdig supports alert blocks as documented at https://github.com/xoofx/markdig/blob/master/src/Markdig.Tests/Specs/AlertBlockSpecs.md.

Bumping markdig and adding `.UseAlertBlocks()` now renders the expected html.

Fixes NuGet#10125

If we don't unset it, the default bootstrap p style turns
dark mode illegible (uses white-ish color). This seems
to be an issue specific to the very old version of Bootstrap
being used (v3.x).

When running the site locally, I could not find any other
.css (or .less) files being built or linked from the page,
so I placed the only needed style in the only other style
file other than bootstrap.