There are plenty of excellent Qt and KDE apps that GNOME avoid using simply because they don’t like the way Qt apps look on their GNOME Desktop.
Well, that excuse is about to expire.
Adwaita-Qt is (as you might guess from the name) a theme that helps make Qt apps look like GTK apps by themeing them to match up with Adwaita, the default GNOME GTK theme.
Or, to borrow the theme’s official blurb, it’s a style “to blend Qt 4 and Qt 5 applications to look like they belong into GNOME Shell”.
To install Adwaita-Qt you’ll need to be familiar with the CMake build system as there are not (at the time of writing) any installer packages available.
Source downloads for Adwita-Qt can be found on Github:
Once the theme installed you can set it as the theme for Qt apps by using the qt-config) app (if installed) or by starting a Qt app with -style adwaita flag.