Unfortunately, GtkFileChooserButton is different from the other
pickers in that it is not a button, but rather has a button.
We ignore the difference for styling purposes, and just add
a .file style class to the button.
<property name="can_focus">1</property>
<property name="receives_default">1</property>
<signal name="clicked" handler="button_clicked_cb" swapped="no"/>
+ <style>
+ <class name="file"/>
+ </style>
<child>
<object class="GtkBox" id="box2">
<property name="visible">1</property>