fix(doc): remove background from operators in dark mode code blocks (#33267)
This removes the white background on operators/strings in code blocks
([deno_doc #742](https://github.com/denoland/deno_doc/issues/742)).
Previous:
<img width="715" height="318" alt="Screenshot_20260413_211537"
src="https://github.com/user-attachments/assets/cc9de06d-dc2e-483c-8cc7-c4715977181a"
/>
Updated:
<img width="715" height="318" alt="image"
src="https://github.com/user-attachments/assets/fbf09373-6211-4379-ab47-af241989bfe0"
/>
Co-authored-by: Jimmy <JimmyBowcott@users.noreply.github.com>