Gtk3 theme development tips

Question

I've started adopting the default Ubuntu Ambiance theme for my needs, but I find it a very cumbersome process. As soon as I change my theme and load it, it also gets cached so any further changes require me to restart the GM (Log out/in, lightdm restart, etc.) This could really take a while and is not really ideal. I've gotten to the point where I test in a VM so I can restart it easily without having to break away from working on the theme on the host.

I've also tried googling and looking up tips for Gtk3 themes on Super User, but there hasn't been a lot published. The only relevant tutorials are for Gtk2 which I'm quite happy with.

So really my question boils down to: are there any ways to speed up theme development? Is there a way to make a CSS chance, launch an app and preview the updates instantly, without relying on restarting the desktop environment?

Answer 1

Per user Gtk3 customization is done in ~/.config/gtk-3.0/gtk.css (to be more precise, in $XDG_CONFIG_HOME/gtk-3.0/gtk.css which usually evaluates to above).

If you want to customize one application, edit and save gtk.css file, then reopen your application. When you are satisfied with results, then you can apply your changes to system theme, or leave it as is.

On Ubuntu update your theme customization will be reverted (if you approve it) if you edited system theme, so better is to copy and rename system theme you like and then customize it; or to customize theme just per one user using gtk.css file in his .config/gtk-3.0 directory.