enhancement: polish lightning and add darkmode background

[VmMad]

Description of change

Move directionalLight position and intensity. Add darkmode background.

Fixes #906, fixes #907

Type of change

• Enhancement (a non-breaking change which adds functionality)

How the change has been tested

Describe the tests that you ran to verify your changes.

Make sure to provide instructions for the maintainer as well as any relevant configurations.

Change checklist

Add an x to the boxes that are relevant to your changes, and delete any items that are not.

• My code follows the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes