docs: code highlight style doesn't display properly in dark mode

[cordeliadillon]

I verified there's no existing issue for this bug.

• There are no existing issues

Current behavior

The .highlight CSS class used in the Skin docs is difficult to see in dark mode. While the text color changes between light and dark modes, the background color stays fixed, resulting in white on light grey in dark mode:

Light mode

Dark mode

Expected behavior

Background color should change to a more suitable color, w/ 4.5:1 contrast ratio against foreground color

Skin version

No response

Device/OS/Browser info

No response

Steps to reproduce

1. Set your system color mode to "Dark"
2. Browse https://opensource.ebay.com/skin/

Relevant code block

No response

Additional context

No response