As stated in style.xml, there is a weird error, which shows Cannot resolve symbol 'Theme', which is quite strange.
See pic of the error :-
My Project Specs:-
Using Android Studio 3.0 beta 4
and gradle version 3.0.0-beta4
Tried clearing the cache by going to File > Invalidate Cache/Restart > Invalidate and Restart, but to no avail, as the error persists.
It seems to be a setting update of "injected references". Search this word in settings dialog and change its "Severity" option to a different value and apply, then change back to its original choice. The error highlight in the editor then disappears.