Raise size of dropdown titles

[theletterf]

Fixes #1919 by raising the size of dropdown titles to the size we use for H4 headings.

+CC @karenzone

[reakaleek]

This looks a bit too big to me.. but I guess that's just my subjective opinion.

[theletterf]

I think an H4 size might make sense considering that we often show these inside H3 (steps) or H2s, instead of fully fledged sections.

[Mpdreamz]

I too think its too big but -lg -base differ too little making -xl the only other option.

Does our text-lg need to be bigger but smaller then -xl and use that?

[theletterf]

We're using text-lg here:

1. src/Elastic.Documentation.Site/Layout/_Header.cshtml:25 - On the logo/home link in the header
2. src/Elastic.Documentation.Site/Layout/_SecondaryNav.cshtml:14 - On the "Docs" link in the secondary navigation

Would it be safe to make it larger for those contexts?

[reakaleek]

I forgot to add text-lg in #2011

I will add it to this PR.

// edit

4ad6abb