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When I have a split layout, the current tab in every group is highlighted in the same way, so the only way to see which tab is the active one is to look for the gutter highlight (or to move the cursor, or to use the mouse.)
Maybe the current tabs in inactive groups could get a "medium highlight", in between the active tab color and the background tab color?
Oh, yeah, this would be very useful for me too!
Do you know if the theme system (or the default theme) has the ability to know which is the active tab?
Looking at the base theme, all the tabs in the split layout seem to render the same, so I'm not sure it's currently supported by ST2.
I'll take a look, but it sounds like a good feature request to throw Jon's way.
I'll close this request for now as I don't think it's something that the core theme engine supports. Feel free to reopen if that changes.
I'd recommend sending a feature request for this to be added to the core of Sublime Text.
Any update to this? Indeed it is confusing, even more when having multiple open groups and clicking in the sidebar on an already opened file. It seems that nothing occurs (because the focus has moved to other group in which that file was alreay opened, but it is hard to realize of it due to the lack of visual indication).
Sorry, I didn't properly realize that this is not feasible at theme level.