the different InputDialog variations all use the Dialog type to provide ready-made implementations for common use-case like confirm(). You can also create a Dialog with custom content yourself in case the ready-made variants do not work for your use-case.The Dialog type offers a default iOS-styled look, based on Theme colors like your Theme.tintColor. The general look of the Dialog is not customizable at the moment.
As an alternative, you can create a fully custom Overlay with the available QML types and controls. (e.g. Rectangle, MouseArea, AppText, etc …).