Remove hardcoded color for settings dashboard

1. Change card_background to default background color. In settings
light theme, background color is exactly the #fafafa
2. Change card_background_grey to colorSecondary, which is
material_grey_200 in settings light theme.

Bug: 36139640
Test: Screenshot
Change-Id: I20081e768985ce6c0b9000448ae48599f18b293a