Default to fully opaque background rectangle

manimlib/mobject/mobject.py

@@ -1436,11 +1436,9 @@ class Mobject(object):
     def add_background_rectangle(
         self,
         color: ManimColor | None = None,
-        opacity: float = 0.75,
+        opacity: float = 1.0,
         **kwargs
     ) -> Self:
-        # TODO, this does not behave well when the mobject has points,
-        # since it gets displayed on top
         from manimlib.mobject.shape_matchers import BackgroundRectangle
         self.background_rectangle = BackgroundRectangle(
             self, color=color,