Update view alpha to improve text color constract in Battery usage

- Update alpha of dark theme from 0.5 to 0.65

[Before] https://screenshot.googleplex.com/3UZicUb7iQa7ovh
A11y Scanner result: https://screenshot.googleplex.com/36wWZDoyJwRy4AK

[After] https://screenshot.googleplex.com/6LRyQMhw2xX6RKk
A11y Scanner result: https://screenshot.googleplex.com/4tWu4RW7VPdJUCP

Bug: 317139415
Bug: 265364351
Test: Accessibility Scanner
Change-Id: I5c1c5c321301da7b148b911a9687a258cc15c87d