See the FAQs for WaveMaker app development.
The Mobile Themes give native look-n-feel of the same page based on the Platform (IOS, Android etc.). Most importantly themes adhere to design guidelines of the Platform, for example, the Page Title in Android platform needs to be left aligned while for iOS it needs to be centered or the menu tab needs to be rendered differently.
Similarly, various widgets like date picker, drop down menu need to be rendered differently based on the platform. All these aspects are taken care of by the inbuilt Mobile Themes provided by WaveMaker.