Document how to find CSS elements to override

[JoelMarcey]

📚 Documentation

https://docusaurus.io/docs/en/api-pages#styles talks about overriding default styles with custom styles, but it does not mention where to go to look for the default styles.

They are in main.css which can be inspected in one of three places:

1. website/node_modules/docusaurus/lib/static/css/main.css after doing a docusaurus-init or yarn install to start developing your site.
2. https://github.com/facebook/Docusaurus/blob/master/v1/lib/static/css/main.css
3. Or you can use your browsers Developer Tools to inspect elements directly to see the name of what to override.

Have you read the Contributing Guidelines on issues?

Yes. I helped write them 😄

[ael-mas]

I'm interested in working on this issue if it is still up for grabs.

[JoelMarcey]

Thanks @ael-mas.

We've added an issue: claimed label so that others will know not to start work on the issue. If you change your mind about the issue, no worries! Just let us know so that we can remove the label and free it up for someone else to claim.

We will check in with you periodically so that we can keep the task updated with the progress.

[yangshun]

Fixed in #1266