Fixed errors in showLineNumbers example.

[beamcode]

The example css did not work properly for conditional showLineNumbers.

Used the css from the website that shows the working example.

• Line 45-53 https://github.com/rehype-pretty/rehype-pretty-code/blob/master/website/src/app/globals.css

Previous sizing of 3rem for 3 digits was too large. Fixed it. Added size for 4 digits.

[Twaites]

Thank you for this! I've spent the last 15 minutes trying to figure out what I did wrong.