Comment 15 for bug 1599453

OK, So I've been having a play with the CSS styling. I've built upon Braden's work which you can see in the additional attached branch. This is a rough and ready POC. But under Ambiance most of the broken backgrounds are fixed. It also includes a cribbed start to making the tab styling follow the GNOME-Terminal tabs under the Ambiance theme. It also includes a fix for the Adwaita overlapping hover area. Stuff still to do:

+ I'm not targeting the specific widgets in just the terminal window yet. That's down to selectors and classes and stuff. For an example under the Ambiance theme the tabs in Prefs get styled like the ones in the terminal window. Need to understand how it is done in GNOME-Terminal, because there it looks like it's pure magic, based on C widget names. Not sure if this works the same in Python. Compare the /usr/share/themes/Ambiance/gtk-3.0/apps/gnome-terminal.css with the newly added terminator.css - we need to get closer to the tighter selectors they have.

+ Ambiance: The very top left and right pixels in the tabs header are still transparent.

+ Ambiance: The Ambiance theme related tweaks file needs to be pulled in as a resource from the appropriate theme directory, instead of brute forcing it in regardless of theme.

+ Ambiance: When hovering over a scrollbar there is a small sliver that becomes transparent.

+ Ambiance: Rest of the tab positions (other than top) need fixing up to also follow the top style.

+ Adwaita: The tabs are transparent still, although we are setting background-color: @bg_color; Maybe Adwaita does not define @bg_color? What does it use instead?

+ Adwaita: There's an unwanted outline in the titlebar.

I really am making this up as I go, so if anyone with more expertise on CSS theming/styling can offer help, it will be greatly appreciated.