WEB: Added stying for pre element within the codeblock divs
- [x] closes ##51657 (Replace xxxx with the GitHub issue number)
- ENH: Enhancement, adding styling (padding and border) for code blocks

I was reviewing the stylesheets. Would you rather have me add the new styling to codehilite.css since it's effecting the codehilite class?
 I ended up moving the css code to codehilite.css  > I ended up moving the css code to codehilite.css

Great, probably better. I'll someone else from the core dev team have a second look and merge, otherwise I'll merge myself in couple of days. But this should be good to go. /preview Website preview of this PR available at: https://pandas.pydata.org/preview/51665/ > Website preview of this PR available at: https://pandas.pydata.org/preview/51665/

An example of where the changes can be seen is here: https://pandas.pydata.org/preview/51665/pdeps/0004-consistent-to-datetime-parsing.html Thanks @dsamuel27, very nice!