[update-theme] Transparent Zen

[sameerasw]

This is a very minor update to fix a background modification being applied to browser dialogs.

This pull request makes minor improvements to the CSS selectors for browser tab tinting in the theme and updates the theme metadata to a new version. The CSS changes make the selectors more specific, ensuring that only direct browser children of .browserStack are targeted.

Theme CSS improvements:

• Updated the .browserStack CSS selectors in chrome.css to use & > browser instead of browser, making the rules apply only to direct browser children for both mod-sameerasw_zen_light_tint="1" and "2" modes. [1] [2]

Theme metadata update:

• Bumped the theme version to 1.17.15 and updated the updatedAt date in theme.json.