Make some things easier to shadow

[jnielson94]

This is a bit of a bigger thing I've run into a few times when I have little tweaks I want to make. For instance, I'm in the process of adjusting my colors to better contrast, but in order to change the global styles I have to shadow the entire Layout file. It seems like it'd be possible to extract the getGlobalStyles function to it's own file, allowing it to be shadowed independently of the rest of the Layout.

I also ran into a similar issue with the home page, which has the Hero component embedded in the file making it impossible to shadow that component on its own and therefore needing to replace the entire index page. I eventually wanted to replace it to remove the pagination of posts and so that I can add other things to the home page in the near future... but that was another example of something that could probably be extracted out to make it easier to shadow specific things. Thoughts?