Change log for 4.0.2 states:
Addons: CSS styles connected via a post template hook did not override the default styles. Fixed.
Nope, just added the my changes css post template hook and tried switching the body background color and it is overwritten by the default styles still.
Firebug shows that my custom css is being added to the standalone stylesheet, but unfortunately it isn't being placed at the very bottom, so some default cart styles are overriding mine still.
Brand new install of 4.0.2 with my changes add on.