Steps to replicate the issue (include links if applicable):

• with dark mode enabled, edit any page that has categories using VisualEditor
• click on the catlinks bar to edit categories
• click on a category to edit its sortkey

What happens?:
The 'tag' icon in the upper left corner next to the popup label is shown in black on dark background.

What should have happened instead?:
the icon should have been inverted.

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):