I attach a theme (for the Basic GUI) I'm working on. This is still work in progress.
This theme provides larger icons for the toolbars. I'm also trying to customize the Qt widgets using a stylesheet (which is very tedious, complicated and boring...)
My intention is not to create something that looks good (I'm afraid I'm very bad at it) but to provide a sample style.qss that others can use as a starting point to create nice themes.