Deprecation of CSS's font-size without unit?

[Jonathan Ballet <jon multani info>]

Hi,

since a few weeks, I got this warning while launching my application [1]
(using Python 3, PyGObject 3.8.2 and Gtk 3.8.2 on Debian sid):

 (sonata:6122): Gtk-WARNING **: Theme parsing error: sonata.css:7:17: Not using units is deprecated. Assuming 
'px'.

So, I implemented a simple fix which consisted of adding the unit (using
'px') to the CSS file [2] and it worked great, but I now have users
complaining [3] that it doesn't work on their computer with Gtk telling
it can't parse the CSS file:

  Traceback (most recent call last):
  ...
  gi._glib.GError: sonata.css:7:17Junk at end of value


I didn't find anything about this behavior in the Gtk/PyGObject
documentation:

* I didn't find a release note in which version not using units started
  to get deprecated
* nor did I find when units started to get supported (since it seems
  it's not on my user's computer)
* and actually, the Gtk documentation doesn't even really say that
  specifying an unit is supported [4]


I'm actually considering reverting [2] but I would like to know if
there's a better to handle this.

Thanks,

 Jonathan


[1] https://github.com/multani/sonata
[2] https://github.com/multani/sonata/commit/293be5
[3] https://github.com/multani/sonata/issues/40
[4] https://developer.gnome.org/gtk3/3.8/GtkCssProvider.html
    in "Supported properties"