[docs] <rh-card>: update Style subpage

[marionnegp]

Images on the Card element's Style subpage are using old color values.

• Update Theme images. Title/header bar uses #f0f0f0 but should be #E0E0E0 for light theme image. Dark theme uses #212427 for header bar, but should be #383838.
• Update Color images. Border color should be #c7c7c7 for light theme. Light gray card in light theme should be using #f2f2f2. Dark theme border should be #707070, and dark gray card surface should be #1f1f1f.