I'm afraid your site is completely inaccessible on my tablet. It appears to be designed for a massive screen and you can't scroll it.
There's some interesting code that allows it to work in mobile friendly fashion on my phone but, I can find no Nabble forum, or if it exists it's been so massively changed by your macro changes for the code to become inaccessible.
In any case your question doesn't make sense. By default a Nabble gallery will display at 100% of the width of the ,"box" in which it is embedded.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.