I don't know any other social media site that allows you that level of freedom of customization.
Reddit used to have custom CSS, still does if you use the old design via the settings or the old.reddit.com address. Check out /r/steam for a subreddit with heavy custom styling.
Sadly in later redesigns they threw that feature out in favor of a more professional but boring looking uniform design.
Some stuff like spoilers started out on the platform using custom CSS. Spoilers used to be done by styling links pointing to a specific address. The worldnews subreddit uses it to hide paywalled articles.