New code theme

[jyecusch]

The current editor theme we use for code fences has a few issues:

• Inconsistent variable colour across languages (e.g. the colour of variables in Go vs JavaScript)
• JavaScript uses green for both variable declarations and strings
• Braces { have no colour
• Function parameters have no colour
• The colour scheme is unfamiliar

We want a colour scheme that outputs code examples similar to how they would appear in Neovim, VSCode, etc. for familiarity. One option to review is catppuccin.

Example

JavaScript

Current docs theme with issues:

The same code using the catppuccin macchiato theme in VSCode:

Go

Current:

Catppuccin: