How to change labels and buttons style for all file but one label?

Question

I am working with a FileChooser module in Kivy which is black by default. But for the rest of my app I used this to define Labels and Buttons style :

<Label>
canvas.before:
                Color:
                    rgba: 1, 1, 1, 1
                Rectangle:
                    pos: self.pos
                    size: self.size 

and

<Button>
    font_size:20
    color:  1,1,1,1
    background_color: (0.55,0.55,0.47,1.0)
    size_hint:0.9,0.2

This is efficient and time saver BUT it breaks the FileChooserIconView I use : The filechooser contains Labels and buttons. They are all in the same class, so do you know how to NOT affect this button and label stuyle to one class ?

I already tried to change the filechooser style instead but it's not working

The filechooser class

<LoadDialog>:
    BoxLayout:
        size: root.size
        pos: root.pos
        orientation: "vertical"

        FileChooserIconView:

            id: filechooser

        BoxLayout:
            size_hint_y: None
            height: 30
            Button:
                text: "Cancel"
                on_release: root.cancel()

            Button:
                text: "Load"
                on_release: root.load(filechooser.path, filechooser.selection)