What makes me feel good in Linux is customization. I've recently tested some great themes for Gnome Shell. They're really great, but sometimes I don't like some part of them. I looked into the files and found out that the themes are CSS-based. I know CSS, but I don't which classes or IDs refer to which parts of the screen.
Is there any reference or guide for theming Gnome Shell? (not GTK3)
This is kind of an old question, Anyway there is a new GTK GUI inspection tool added with GTK v3.14.
Source: Gnome Projects: GtkInspector
It is more convenient to know the runtime GUI shell directly than following code, as many applications out there using chunks to construct GUI dynamically.
I didn't need to use the shortcut running for example
GTK_DEBUG=interactive gedit
brings up the GTK Inspector.while i also have failed so far to find some type of cheat-sheet for gnome 3.4 themes the posts on the blog of fp.murphy where Lucas Romero already has linked to seem to contain plenty of very useful information regarding gnome 3.x and its customization.
some basics worth reading prior to the post provided by Lucas can be found in an ealier post there giving some simple examples and general overview.
if more specifically geared to gnome shell extensions i found the series of up to now 4 posts all written in september 2012 on mathematicalcoffee very helpful. since gnome 3.4 has brought many api-changes its important to look into recent information regarding gnome customization.