docs: 4.0 fixes

[yggg]

Please read and mark the following check list before creating a pull request:

• I read and followed the CONTRIBUTING.md guide.
• I read and followed the New Feature Checklist guide.

Short description of what this resolves:

Make example background same as layout background.
Make concave same color as layout.
Fill extra space with component cards.
Make example fit in small screens.
Remove window background.
Remove unnecessary spaces.
Remove card shadow.