How can I enable an effect similar to Aero Glass in Windows for window's titlebars without switching the default Breeze theme?
It can be done pretty easily in Unity/Compiz by
metacity-theme-inactive-opacity keys of the
org.compiz.gwd schema. This will produce the titlebar effect looking like this:
In KDE4 this effect definitely existed also. This can be seen on screenshot found on Mint forums:
But KDE Plasma 5 hasn't got Decorations slider in the options of the Translucency effect which can be found in System Settings > Desktop Behavior > Desktop Effects (I am using Ubuntu 16.04 with KDE Plasma v5.5.5).
I am aware that people somehow change the transparency of the panels by editing proper SVG files of the theme (though there's a method which is more simple than that).
If you direct me which file(s) of the theme should be altered to gain titlebar transparency I'd also accept it as an answer, if no easier methods exist.