Add focus state for selected & active tab

Now:

Should be:

More details: https://forum.sublimetext.com/t/release-v1-1-0-otto-your-next-theme-for-sublime-text-3/18244/17?u=oivva

[FichteFoll]

I generally support this. However, your example would imply that the tabs of inactive groups are also inactive, meaning some other tab would be active but there is none.

Imo there should be a different kind of visualization for inactive groups, which is why https://github.com/SublimeText/InactivePanes/ exists (as mentioned in the referenced thread), but if it's themeable then pretty much anything's possible.

[wbond]

In general I think the proposed screenshot isn't a great idea. It shows the content of two files disconnected from their tabs. It may not be obvious with "untitled", but it would be odd to have multiple files in each pane, and be showing the content of one, but having no idea which tab the contents are from.

I think if this were to be implemented, it would have to be done in such a way that a "focused" state was added to one View per Window. And it would need to be distinct from the "active" state that currently is used to render tab sets.

[UltraInstinct05]

Build 4095 now adds dimming of inactive panes to the core with the addition of the background_modifier property to be used via themes. So inactive panes will be slightly dimmed out and thus the active view/pane is more visible/stands out better in multi pane layouts.

[deathaxe]

Closing it as duplicate of #3148 because that issue containes more information and is marked fixed already