Adjust screen width breakpoints and misc fixes

[sfc-gh-dmatthews]

📚 Context

As screen sizes grow larger, comfortable page widths increase. This PR adds a few more break points/screen sizes to increase the maximum page width.

🧠 Description of Changes

• Added "3xl" screen sizes. The body of the page and the table of contents will increase in width at "3xl."
• Fixed alignment of left navigation in a narrow band between "lg" and "xl" screens. This is about restoring alignment within the original design, but the "condensed" menu that exists between 1024px and 1250px screen width needs refinement.
• Fixed hover text on theme mode selector (now shows the name of the mode to switch to).
• Fixed breadcrumb contrast in dark mode.

New:

Previous:

🌐 References

Notion project: Docs papercut: Alignment of left navigation

Contribution License Agreement By submitting this pull request you agree that all contributions to this project are made under the Apache 2.0 license.

[sfc-gh-dmatthews]

Looking again, "4xl" pages are probably too wide when there isn't a TOC. That size looks okay on "full" pages, but it's too stretched on when there's no TOC. Maybe I can take off that largest size and only introduce the "3xl" for now?

/develop/concepts/architecture/widget-behavior looks okay at the "4xl" breakpoint, but the homepage is too stretched without a TOC on the right.