New default theme...

[tomchristie]

Escalated from discussion #3661

・・・

I've spent a bit of time considering a re-working from scratch, but perhaps we should start with some simple iterative improvements to the default theme?...

• The current coloring is just too loud. Here's a more muted darkslateblue, without the unnecessary gradiant gloss.
• Drop the previous and next controls from the nav bar.
• Drop the text from the search/repo/color mode.

---

・・・

• Less verbose search modal.

---

・・・

• Bring transparency to the table of contents.

[pawamoy]

Looking good! If you want to draft a PR I (and others) can test it locally :slightly_smiling_face: