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.