WEB: Improve the style of the code boxes in the website #51657
Description
xref #51458 (comment)
In our website we've got a style for the boxes with source code. I don't think we've got many, but at least some PDEPs do, see https://pandas.pydata.org/pdeps/0004-consistent-to-datetime-parsing.html
It'd be good to get the formatting of the code blocks nicer, with padding, and maybe a border. Also the quote blocks can probably be improved.
The styles should be defined in web/pandas/static/css.