I previously wrote about some appearance-related changes I’d made to my IceWM installation. At the time I’d installed packages oxygen-icons, xcursor-vanilla-dmz, and gnome-icon-theme, and then made them active by manually editing files. The results were an improvement over the default settings but most programs still looked rather unattractive. Also, in some cases the font was too big and text was truncated as a result. I found a better answer on the GTK+ page of the Arch Wiki.
Per the wiki article I installed additional packages lxappearance and gtk-engines. I also installed cantarell-fonts, which isn’t required but seems to be the default font for the standard GTK+ themes.
lxappearance is the appearance manager for the LXDE desktop; however, it’s powerful and works with all desktops (it doesn’t have any LXDE dependencies).
lxappearance didn’t show up on my menu so I ran it from a terminal:
Using lxappearance I was able to set a few things that I hadn’t been able to set before, including the font size. When I was done I clicked the Apply button, which changed my desktop background color to gray. Logging out and logging back in restored my desktop background.
Making these settings improved the look of GTK+ 2 applications. Presumably it doesn’t have much effect on GTK+ 3 or Qt applications but so far I’m happy with the results.