[docs] CSS style improvements

[timhoffm]

As a suggestion:

• increase paragraph line-height to 1.5 to give text a bit more room to breathe. 1.5 is a common choice in web page typography; e.g. rtd-sphinx-theme, furo and GitHub use this (pydata sphinx theme goes even to 1.65).
• Don't shrink the text in admonitions. They are equally important and thus should have the same size as regular paragraphs. For reference, e.g. pydata-sphinx-theme and rtd-sphinx-theme do this.
• Adapt the border color for all warning/error like admonitions. Warnings had a fixed color that did not fit well to the new admonition style.

[chrisjsewell]

Don't shrink the text in admonitions. They are equally important and thus should have the same size as regular paragraphs. For reference, e.g. pydata-sphinx-theme and rtd-sphinx-theme do this.

For counter-reference though 😅 : https://pradyunsg.me/furo/kitchen-sink/admonitions/ and https://squidfunk.github.io/mkdocs-material/reference/annotations/, the text is smaller

They are meant to be "asides" semantically, so I don't know if I agree that they are "equally important" (and I think in general furo is nicer looking and maybe better to follow)

If nothing else, the "feature" admonitions on the landing page should still be smaller.

The other changes I think are good 👍

[chrisjsewell]

see comment

[timhoffm]

Re: Font size of admonitions:

I believe we're all not experts on typography. I therefore checked what "big sites" do, assuming they have thought about these things.

Note

GitHub does not reduce the font size in admontions.

The same holds for Microsoft Azure docs and Apple developer docs.

Based on that, I propose same-size is likely better, but I don't have a strong opinion.

[timhoffm]

If nothing else, the "feature" admonitions on the landing page should still be smaller.

Ok, kept them in the smaller font.

[chrisjsewell]

I removed the increase in admonition text size for now, since I really do feel it makes the pages with many admonitions less readable