Due to the pluralism embodied in Linux software design and user proclivity, window styles for applications developed with different GUI frameworks are controlled and exhibited separately. Therefore, in my KDE environment, the look-and-feel configuration of the workspace theme is only effective for KDE applications such as Dolfin, Konsole, etc.

To make it applicable to GTK applications, we need to further open the configuration dialogue in System settings → Appearance → Application Style → GNOME Application Style (GTK), and set the GTK application styles to be the same as KDE, for example, workspace theme, default font, toolbar style, cursor theme and icon theme. Then, the display styles for all opened windows will be consistent.

Figure Configure GTK application styles to be the same as KDE.