I seem to be somewhat addicted to the SlicknesS-black theme, but one common problem with dark themes is that they often render certain programs virtually unusable (or at the very least, much more difficult to use), OpenOffice Writer being what prompted me to discover the fix for this as under the SlicknesS-black theme it is impossible to change the color of the text.
One fix was posted on the gnome-look website, but several comments were posted that it didn't work (which I can confirm; it really didn't work, not on my computer at least). I give that fix credit for pointing me in the correct direction, but ultimately a different technique was needed.
This howto isn't just for people having issues with dark themes, though. If you've ever wanted to run one application using a different theme than the rest of your system (or hell, choose a different theme for each application. Why not?), it's actually very easy.
The basic idea is to create an executable shell script that will override the program's launching script in order to call that script using the env command. For this howto I'll demonstrate how I used this technique to run OpenOffice using the SlicknessX theme (although any theme with a locatable gtkrc file will work).
Here we go.
1) First, find the exact location of the executable that calls the program that you want to theme. This can be done using the 'which' command. To find OpenOffice, you would type into the terminal: 'which ooffice'. This gave me the result '/usr/bin/ooffice'. So far so good.
2) Second, check on your PATH variable. For this to work you need to settle on using a directory that's higher up on the search path than the one where the executable currently resides (in this case, '/usr/bin'). You can see your current value for path by typing 'echo $PATH' into a terminal. To be higher up on the search path, the directory you want to use should be to the left of the one that contains the script's executable. I highly recommend creating a bin folder in your home directory and setting that as the top folder in the search path exactly for situations like these. To do that:
Close the terminal and open it again, then check on PATH by typing 'echo $PATH' again. If the first value isn't /home/YOUR_USERNAME/bin (my terminal automatically added my home bin folder to the path), you'll need to put it there manually by opening up .bashrc ...
... going down to the bottom of the page, and entering in this line:
Again, you can use any directory as long as it's higher up the search path than the program's executable, but the rest of this howto will assume that ~/bin is being used.
3) Okay, now we'll create the script that will override the program. To override OpenOffice's executable (/usr/bin/ooffice), create a file called 'ooffice' in ~/bin:
The actual script we'll put into this file is very simple, but we need some information first. Namely, decide on a theme to use, and then locate that theme's gtkrc file. Themes are usually installed in /usr/share/themes or ~/.themes. Open up the folder for the one you want, open up the 'gtk-2.0' folder, and make sure that a file called 'gtkrc' is in that directory. If it isn't, choose a different theme; if it is, remember its absolute path (in my case it's '/usr/share/themes/SlicknessX/gtk-2.0/gtkrc'). In addition to that you'll need the absolute path to your program's executable ('/usr/bin/ooffice'). Once you have that, put this in the 'ooffice' file we created:
$ gedit ~/bin/ooffice
Since this technique can be used for any program, here's the basic format. Remember, the filename must be the same as the program's executable script (what you would type into the terminal to open it):
env GTK2_RC_FILES=/usr/share/themes/SlicknessX/gtk-2.0/gtkrc /usr/bin/ooffice "$@"
4) Last step: make our newly created script executable. To do that, simply type this into a terminal:
env GTK2_RC_FILES=PATH_TO_GTKRC PATH_TO_EXECUTABLE "$@"
This step is extremely important, since without it our newly created script would be unable to execute.
$ chmod +x ~/bin/ooffice
Now every time you open OpenOffice (or whichever program you desire to theme), it will open in the chosen theme. If you want to undo this it's as simple as removing the script (rm ~/bin/ooffice).
Feedback is welcome.