changed homepage bg colour from white to #f8f8f8

[warren-davies4]

❓What: Changed background colour on home page from white to #f8f8f8 (light gray, matches rest of site)

🧠Why?: Accessibility

👨‍💻How?: updated CSS class container--white

Checklist:

Have checked for the following: Yes

• The website still builds correctly, and you can view it using mkdocs serve.
• There are no new "warnings" from mkdocs
• Does your page follow the page template (or here in Markdown)?
• Spelling errors
• Consistent capitalization
• Consistent numbers
• Material features incorrectly implemented: search for code blocks and markers (e.g. !!!).
• Code snippets don't work
• Images not working
• Links not working

Where it was tested

• Github Codespaces - 2-core, 4GB RAM, 32GB hard drive
• devcontainer.json describes further settings

[simonechung]

Blend white box on What is RAP? section into updated background colour where possible.