I am just about to migrate from old Ubuntu 10.04, which I was using for many years, to Ubuntu MATE 18.04 (didn't install it yet, until now just playing around with live DVD). I liked very much my old desktop layout from 10.04 and I want a similar layout in the new system.
By trial and error (as I can't find any documentation for this) I created my own desktop theme by combining some files from Radiant-MATE theme, Radiance theme from original Ubuntu and my old theme from 10.04 (which was gtk2 only). Still some applications aren't using that theme (eg. Firefox in no title bar mode uses minimize/maximize/close icons from the original Ambiant-MATE theme, even after I deleted - for testing - this theme from the system (in fact I deleted ALL themes except the one I created), similarly does dconf-editor - I don't understand this), but for now I can live with this. I also changed system fonts (Appearance -> Fonts) and some application settings eg. default color scheme in Pluma and terminal, changed the panel layout to Traditional etc.
The question is - I want to make these changes a new system-wide default, so that they will be applied for any user (including any newly created account) automatically.
After searching the net I dind't find any clear explanation how to do this, so I'm asking here. Assume I have set all desktop and applications details on my account as I need and now want to "promote" these settings to become a system-wide default. How do I do this?
Also - is there any way to change the font and color scheme that slick-greeter uses on the login screen? I set it in dconf-editor to use my desktop theme and a font I chose, but the theme and font is only used for the top-right corner menus: accessibility options and shutdown/reboot/etc. The style of the top panel (colors, icons etc.) as well as the main font used on login screen did not change. Is there any way to change this?