Inserting the code you propose is not as simple as "<body> my code here... ". We need to know what app type you are using and consider every different type of page that app uses.
However, I'm not clear why you want to do this. Normally there is no reason for it as Nabble is designed to be embedded in other sites, and it is expected that the navigation system would be coded into the host site, not into a Nabble forum. Why do you need to do it a different way to that for which Nabble is designed?
My issue with embedding is the search engine... The one which will appear in searches will be the main forum and not my main site... The main forum that will appear in searches are not well-designed that viewers will not be linked to my main site... I can't explain it briefly but hope you get what i mean...
My forum is embedded on the first/home page of my site, but there are another 425+ pages of documentation beyond the forum. And a Google search will, now, find things in my forum as well as on the rest of the site.
Having said that, Google's indexing of the forum itself isn't rapid. But it does happen.
Oh yah... I just tried your site and tested 1 specific post in your forum for search index... But the redirect is somewhere between 0.5-1 sec. I think too many redirects are not good SEO... I just need to install my navbar... If I have my navbar installed, then its easy for me to design the forum since the CSS are pretty well accessible.
My Nabble forums are mostly embedded in hobby sites and I don't worry about search engines finding every Nabble page as users pick up the main sites from the the search results and on visiting the main encounter the forums and can use the internal search if necessary. However, I do understand that it's more important for others.
The obvious place to start is the "Edit this page" link, then click "cog wheel" button and on the menu that appears click on "Search macros".
On the Macro Search page, enter "<body>" without the quotes and check the option "Macro source contains" before clicking the "Search " button.
On Nabble Support (and probably your forum too) it turns up 88 hits. It's then just a matter of looking at each of those macros and working out if you really need your navigation code on everyone one of them or only some! (I suspect relatively few of them as many will be related to specific Apps,)
Your code also had reference to various CSS classes. Installing them should be somewhat easier. Go to:
Options > Application > Change Appearance > CSS
and enter your styling code there. (There are some cases where I found that I needed to provide a conditional ".nabble" selector but I can't remember what those circumstances are at the moment - and having just looked at the code behind one of my forums I realise much has changed under the hood compared to the last time I looked.
I repeat, this is definitely not a simple project!
My web hosts include a package called "Softaculous" See: http://www.softaculous.com/demos Makes it dead easy to install all kinds of site building and embeddable tools including a good number of forum software. I suspect it would be easier to work with one of them because they are designed to be installed by coders and usually have reasonable documentation and support networks.
Trying to reverse engineer Nabble to work out how to make the kind of customisation that was never envisaged by them is always going to be a lot harder.
Sometimes I wish I wasn't so negative! My wife complains I'm a "glass half empty" kind of guy - never half full!
Just a Volunteer Nabble Helper - because the nice folk at Nabble have helped me! GregHelp - Building a set of answers to Nabble FAQs.