Additional docs site look-and-feel updates

From the CEO livestream, the following docs site style updates would help the site be more appealing to site visitors viewing product documentation pages:

• Add additional whitespace between the global navigation, content, and table of contents sections of the page. Refer to the Stripe documentation for guidance. In progress
• Change the background color of the global navigation and the table of contents both to white (the same color as the background of the content). Done
• Evaluate the use of a different font for the docs site, and make the change (once identified). In progress
• In the table of contents for documentation pages, remove the horizontal line that separates "Help and feedback" from the other table of content items.Done

Feel free to create MRs as needed to address these issues (including MRs that may combine items to be changed).