toggle color of cfg button depending on state

frame.py

@@ -49,11 +49,16 @@ class Frame:
         self.btn_close.on_click(*args, **kwargs)
 
     def do_click_cfg(self):
+        toggle_button_type(self.btn_cfg, "default", "warning")
         self.inner.visible = False
         switch_visibility(self.plt.fig, self.cfg_dialog)
         self.inner.visible = True
 
 
+
+def toggle_button_type(btn, type1, type2):
+    btn.button_type = type2 if btn.button_type == type1 else type1
+
 def switch_visibility(a, b):
     a.visible, b.visible = b.visible, a.visible