It really depends on the layout. What I typically do when I want to figure out what the class or id name is for a specific area is view source, then ctrl+f for what I'm looking for - for example, the sidebar - I'll search for some text that I know is in the sidebar. Then when I find it, I scroll up a little bit, and when I see the div containing the sidebar, it should say something like the following:
As you know, you would insert #idname or .classname into the code related to the part of the layout you're modifying.
The same would apply to the icon. If you can see any classes or ids for the div containing the icon, or even the icon itself, that would be a good place to start.
The classes definitely do change depending on the layout you're using, in both S1 and S2. http://journalhelp.com
has a lot of help relating to "what does what".