Where to see the prefix of the content container

I have installed a plugin called Hammy, that should improve the load on pictures. But I need to do this:

) Enter your Content Container

Add the content class or ID that is consistent across all templates (i.e. on every page and post), oftentimes named #content or .entry-content, etc. Make sure you use the approriate prefix.

Where do I see my content container. I has made a default choise. It is ".entry-content" Can I be sure that this is the right one for my Buddypress Default theme? Or could it also be "#centent" I hope you can tell me, where I can see, what my content container is called.