There shouldn't be any issues with .svg or .png - I use them interchangeably.
When you go to change a panel icon (via right click > Properties and click on the icon button) you bring up the Browse Icons window. At the top right of that is a Browse button that will let you select an alternate folder from which to choose icons. There is no restriction on which folder you can choose.
Most icons are in folders below /usr/share/icons. The icon sets are one per folder, with sub-folders for things like apps, emblems, mimetypes, status, etc. There may be sub-folders for different icon sizes (e.g scalable, or 48x48) - you'll figure that out, I'm sure. Not all icon sets are complete - you can see that for yourself if you browse through those folders. But you can address that by specifying "inherits" for the icon theme.
The icon theme can be changed via the main menu: System > Preferences > Look and Feel > Appearance and select the Customize button and then the Icon tab to pick a new icon theme for whatever desktop theme you're using. You can save any particular icon theme as the default for a desktop theme for your user - just save the customised desktop theme (via Save As) and give it a name - it''ll save that in folder /home/<username>/.themes, i.e. only available to your user account. You can make it a system-wide change by editing the theme specification - more on that later.
Icon themes are specified in each icon folder (e.g. /usr/share/icons/Tango) in a text file (index.theme). To open such a file, use the command line as root, e.g.:
Code:
su -
gedit /usr/share/icons/Tango/index.theme
At the top of the file (usually the fourth line) you'll see the specified icon theme inherits - these are simply the names of themes, in order of preference, that your system should fall back to when trying to find an icon for a particular object. For example, if in the Oxygen icon theme.index file you specify these inherits:
Code:
Inherits=Tango,gnome
... and there's no icon given in Oxygen, your system will search the Tango theme, and if it doesn't find it there, it will search gnome theme, and so on. BTW, the official name of the icon theme, which you may need later, is given in a line like this:
The objects (for which icons are assigned) are named according to the freedesktop.org specification - a standard object name or, for a specific application, the application executable name.
You can read the specification here: http://standards.freedesktop.org/ico...ec-latest.html
If you take a look at the Standard Place Icons section of the specification, you can see it specifies "user-trash", which is the empty trash can icon. Now take a look at the Standard Status Icons section, and you'll see "user-trash-full". The Oxygen icon theme does have icons for both, so I'm betting you manually changed the desktop trash icon (by right-clicking on it) instead of changing the icon theme. To correct the problem, just change the icon theme (as described above). Any manually changed icons will have to be changed to their theme defaults if they're misbehaving.
Desktop theme specifications are defined similarly to icon themes, but in /usr/share/themes. I won't go into the details, even though I've been editing gtk and metacity themes lately, just for kicks. The important point is that you can specify a default icon theme for a desktop theme via the file index.theme. For example, for the desktop theme "Crux", there is a corresponding icon theme also called "Crux". You can change it by editing the file:
Code:
su -
gedit /usr/share/themes/Crux/index.theme
... and, usually right at the bottom, you'll see the line to edit - use the icon theme's official name:
That ought to be enough for now. Have fun.