docs(styles): import styles globally rather than in the index.mdx file

@flpm mentioned in this issue
https://github.com/all-contributors/all-contributors.github.io/issues/903

that the relative paths in our index.mdx files were causing issues with translations. This is actually a great point to address because the style sheets were messy and it's easy to setup styles globally. This is an easy fix so I will open a PR to address it.