Can I apply a different GTK3 theme from the main one to an individual application?

Question

For example, can I keep Ambiance as main theme but assign elementary theme to elementary's app?

Answer 1

Yes, the simple way is to point the application at the required path where your rc file lives, in the command that runs your application:

GTK2_RC_FILES=/usr/share/themes/Redmond/gtk-2.0/gtkrc inkscape

This on 12.04 for inkscape (which is still Gnome2 btw) produces this:

See more information about Gtk2 theme running here.

Answer 2

Yes you can, actually I googled and got some answers:

1. Look for the exact executable for the program you want to change the theme. for example, if you want it for ooffice then type which ooffice in the terminal.
2. Look for the bin folder where all applications put their binary executables. Type echo $PATH in the terminal and you will ge the path. I recommend you to create a bin folder in your home directory by typing mkdir ~/bin
3. Type gedit ~/.bashrc to open your bash rc file.
4. Go to the bottom of this file and add this line export PATH=~/bin:${PATH}

No we will create a script which will execute your program with custom theme:

1. Create application's script file by typing: gedit ~/bin/ooffice

2. Type these lines in the opened file:

   1. #!/bin/bash
   2. env GTK2_RC_FILES=/usr/share/themes/SlicknessX/gtk-2.0/gtkrc /usr/bin/ooffice "$@"

3. Change the mode of the file to executable by typing: chmod +x ~/bin/ooffice.

Hope this helps, you have to remember only one thing, the format of the script as shown below:

#!/bin/bash
env GTK2_RC_FILES=PATH_TO_GTKRC PATH_TO_EXECUTABLE "$@"

Answer 3

Its certainly possible, I don't have much of themeing experience, but when you navigate to /usr/share/themes/*Theme Name*/gtk-3.0/apps/ directory, you'll find .css files, named with apps they target, to theme, so yes you can create the Themes.

Note that the way you mentioned to theme your apps may require some work to be done (like having both Ambiance and Elementary work simultaneously, since every theme has a base file on top of which app specific styling is done, (a file gtkrc in Gtk 2.0 while, a file gtk.css in case of Gtk3.0).

And this base theme file contains styling rules that specifically target the given theme, hence you cannot create Elementary like look and feel from Ambiance's base theme file without making some have changes, and even if you do, you'll loose Ambiance look itself.

Also, in GNOME, it is possible to have only single theme applied at a time, For Example, if you have used Appearance window in Ubuntu 12.04, you know can can select any single theme from the dropdown, in case you have used gnome-tweak-tool, than you can set different themes, for Gtk, Window frames, and icons, but still, it doesn't allow to target specific applications to theme, so as I said earlier, you can set totally different themes for different applications if you cleverly work with base theme file, as of now, no third party applications can do it by itself.

One way you can do it by yourself is that, let the base theme file (gtk.css) have only essential rules which are neutral to any theme, being dark or light. And have the actual theme design written in app-specific files that reside in above mentioned directory, i.e. for styling Nautilus, you can write all required properties in nautilus.css file. Same with every app you wish to target. Obviously, doing such requires some decent Gtk themeing experience.

You may refer this for creating your own theme using template, Also there's a decent documentation on Gtk+ themeing.