Gtk stylesheets(themes) are not dynamic… so there isn’t a single place that you can change things on the fly.
Stylesheets need to be changed either manually or via a scripted method and then installed … and then you need to logout login for changes to take effect.
So any “app” will effectively need to make the changes, compile the theme and install.
What i’ve done is copying the Pocillo folder (renamed it) and played around with the gtk.css inside the gtk-3.22 folder. Than i copied the folder inside my ~/.themes folder and applied via the Budgie Desktop Settings Application. Nothing happened. Maybe i’ll take a look at the Documentation:
https://developer.gnome.org/
You need to flip between themes to see changes
E.g. this is a simple script we use when amending and testing pocillo
So, that is actually what i did, too - except putting it in a script. I switched in the Budgie Desktop Application the themes forth and back, no changes.
Do things in the terminal. Often errors show up in the terminal that you wouldn’t see via the GUI.
Anyway … this is off topic. Please raise a separate topic if need be.
A new Ubuntu Budgie Theme for GTK4: why not ask our best pal Vinceliucie for a new Budgie specific set of themes? He IS the king, after all 
Some are near ready for Yaru ( not gtk4 though ).
The @ubuntu_mate team have also been collaborating with the Yaru team 🥰 We'd like to invite 🎟 you to test our daily images ahead of the March 18th UI freeze 🥶 too https://t.co/XlAfGKjsj6 https://t.co/7t5OeXnVUI pic.twitter.com/MFUmbuUp35
— Martin Wimpress (@m_wimpress) March 7, 2021
I like Pocillo fine. I don’t really have complaints. If this is changed, I am sure I will lol.
Do you think there is no chance Pocillo will get GTK-4 support?
My first thought was ask around to see what other distros are doing as far as this goes. Like for example, like Ubuntu Mate. That one just comes up for me because it is also Ubuntu base with a different desktop environment and was kinda next down on the list of distros I liked.
For me, everything about Ubuntu look/feel/nav/flow to me seems like it belongs on a tablet. I might would like that I guess if I walked around half the day on an android tablet and wanted my laptop/desktop to be similar. But I don’t.
As mentioned, I would like to see a new dedicated team member to run with this. So if they choose to just add Gtk4 support then great. If it’s chosen to use best in class like Yaru then i bow to their judgement.
If no one steps up then we will have to take the least risk solution which would be to use an existing well maintained theme … maybe with a few tweaks and tucks if necessary.
Gtk4 isn’t really about making things like a tablet. One area it does allow is that apps can adapt much easier to different form factors.
Well right now no but in the next weeks, I guess that the guy that made the theme de Mojave will update your themes.
Whitesur GTK4 support
Mojave
One background task I’m considering is relooking at the original predecessor to Pocillo which was called materia (its in themes & layouts)
It has recently had its GTK4 support updated.
The colours will need revisiting - but thats most probably just updating the colour values here
Anyone willing to help fiddling here would be most appreciated.
Just a little input here, Ubuntu Mate worked with the Yaru team to create a Mate coloured version of Yaru. So some others are also going that way. I like using this theme (as a base) because the dev team is super active. Probably more active than I have seen on other themes. I also believe the Yaru team is more than a single person. 
I don’t know what to think about that but it’s also about the future of theming :
And Yaru + Mate becomes a reality
Ok. The initial discussions on the Yaru github tracker do sound promising. So cross fingers that progress could be made here.
In addition I have been revisiting the idea of rebasing Pocillo back on the original upstream Materia.
This is working pretty well now for the dark variant and now has full Gtk+4 support.
If you want to follow along - and help out? - GitHub - UbuntuBudgie/pocillo-gtk-theme: GTK+ 3.22 based theme for the Budgie Desktop that has Material Design elements and styled using the Arc colour palette … if installing the temporary theme name is “NewPocillo”
Taken together we have two possible routes for 21.10
Closing this - seems to have run its course.
Assuming Yaru effort progresses then we’ll have a testing topic.
For Pocillo Testing the new Pocillo theme
