Allow addition of a Stylesheet + Submit as Theme
I would like to be able to include a stylesheet of a custom theme I make for the slideshow. A simple "Custom Stylesheet" box would suffice for this.
Also, I think it would be nice if I can submit that stylesheet as a theme to help expand the themes for all users. This can be categorized as "User Themes" so they know there is a risk of cross-browser support, etc.
Custom CSS is now available as an option in editor’s Style panel for Pro users. There’s a bit more info in this blog post http://blog.slid.es/post/56336481462/update-pdf-export-background-images-and-custom-css
As to the second point, a user-submitted theme gallery isn’t in our plans at the moment.