Add light theme to documentation website

[failable]

Please describe your idea in depth. If you're not sure what to write, imagine the following:

• How is this important to you? How would you use it? Important, use it daily as a new beginner to robin.
• Can you think of any alternatives? Chrome extension does not work well.
• Do you have any ideas about how it can be implemented? Are you willing/able to implement it? Do you need mentoring? Not sure.

[thePromger]

@failable

• dark theme have less strains on eyes, so for now its fine

if you want to work on it, then you are welcome but for now its not in our prioprity list