as it seems custom CSS is not applied to shared lists, so you can only share your content, but not how you styled it. Is that intentional?
(If this is somehow to prevent circumventing the PRO-only restriction, IMO there is no reason not to apply custom CSS at least to read-only shared lists.)
The shared list has the public URL https://checkvist.com/p/UV9IHRjo2QWFWQqS5rszuS. If I open that URL while being logged in to Checkvist, the custom CSS is applied and the list looks just the same as above. However, if I open that URL in a private/guest browser window or after having logged out, the list looks like this:
So, yes, the custom CSS is applied to shared lists, but only for me, not for someone I share the list with - at least if (s)he has no Checkvist account or isn’t logged in (I don’t know, and cannot find out, what the list looks like for someone who has a Checkvist account and is logged in, but did not set the same custom CSS).
I’ve opened the shared list in https://beta.checkvist.com and obtained the public URL https://beta.checkvist.com/p/UV9IHRjo2QWFWQqS5rszuS. Unfortunately, if I open this URL in a private browser window or after having logged out from Checkvist, the custom CSS (which works when I open the list while being logged in) is not applied to the list, as the list is displayed in standard black letters (instead of green monospace letters). I suppose you can confirm this by yourself by following the above link.