Grey out unfocused window title bar text in GTK4 theme
Currently in the GTK4 theme, title bar text remains the same colour (~ black for the light theme, ~ white for dark) when unfocused. Especially for the dark theme, this makes it much less obvious that the window is unfocused, which can result in e.g. mistakenly sending keystrokes to the wrong window with the assumption that the unfocused window is the one that has focus.
In contrast (sic!), with GTK3, title bar text becomes grey when the window is unfocused, which makes the focus state much more obvious.
GTK4 dark theme focused/unfocused screenshots:
Focused:
Unfocused: