Prettify the website

[PaulRBerg]

What we should do:

• [ ] Design the landing page
• [ ] Use our primary color less often (e.g. don't use it in hyperlinks anymore)

Potential inspiration:

• Uniswap Docs
• Balancer Docs
• 0x Docs

[PaulRBerg]

The default dark theme for code blocks looks ugly:

https://sablier-v2-docs.vercel.app/contracts/v2/guides/local-environment#sample-contract