GitLab

Traceback (most recent call last):
  File "/home/vlopes/git/gnome-layout-switcher/UI.py", line 241, in on_color_chosen
    Backend.set_highlight_color(col)
  File "/home/vlopes/git/gnome-layout-switcher/Backend.py", line 87, in set_highlight_color
    shutil.copyfile('/usr/share/gtk-3.0/gtk.css', get_user_gtk_css())
  File "/usr/lib/python3.7/shutil.py", line 120, in copyfile
    with open(src, 'rb') as fsrc:
FileNotFoundError: [Errno 2] No such file or directory: '/usr/share/gtk-3.0/gtk.css'

FIX: check if file exists before copying, add a try block with an exception FileNotFoundError, level easy.

This one is easy will give it to you as a learning opportunity @Chrysostomus, if you need help let me know.