Align button to bottom left corner

I have a Canvas with fixed height

i want to align my buttons to the corners
The buttons are not directly on the Canvas, they are within different nodes
Eg:
Canvas
Holder
Button

I add a widget to the button
I set left and bottom check boxes and set the target to Canvas

When I run the game, the button is not getting aligned to the bottom corner.

If the button is on the canvas it works

Can anyone advice why this is happening?