Hello,

Yes, the reason in mainly due to the fact that the same classes names are loaded too times.

To have 2 or more different theme pack in the same page, you will have first to use page classe suffix in your menu.
For example : " myclass1"

Then, you will have to create new themes (dupplicate the official one, and change the names of the theme in file names and inside names, with your own name (for example, replace all "ic_rounded" by "my_custom_theme") and add prefix to classes names.
Or to add custom css with prefix in the template css file. (this don't need to create custom theme packs).
For all classes, add ".myclass1 " before each styling css

In all cases, needs to not have the same classes names for the 2 theme pack, or to use a menu prefix classe and change one of the theme pack CSS.

Hope this helps... and not too confuse, as in fact, many way to do this...

Regards,
Cyril