We are happy to announce that the discourse-styleguide plugin has been merged into Discourse Core!
To enable it, search styleguide
in your admin settings, and click to enable.
This will allow you to visit yoursite.com/styleguide
which will render Discourse components and widgets in various configurations to aid in styling.
This helps a ton when designing custom themes and specifically targeting some of the less seen elements of Discourse.
Some examples of what you can find at /styleguide
include the following + many more.