I have a similar problem too. I want to change the font size and I get a fallback base style.
I've already reported a bug against Qt. Maybe we could find another workaround in the meantime.
All the android styling seems done by the AndroidStyle singleton object coming from QtQuick.Controls.Styles.Android 1.0 module.
They do, for example
Style {
readonly property Button control: __control
property Component panel: Item {
id: panel
readonly property var styleDef: control.checkable ? AndroidStyle.styleDef.buttonStyleToggle : AndroidStyle.styleDef.buttonStyle
// some more code
}
see ButtonStyle.qml
But, if we look further, styleDef seems specific to the Android drawables, see this commit
And the Android Button.qml seems to use something like this for setting the style
style: Settings.styleComponent(Settings.style, "ButtonStyle.qml", button)
But I don't know where the settings come from
See Button.qml
Do you have any idea what to do with it? I don't see any other option that copying the Android Styles tree and adapting it to our needs. But it's awful.