header info display color in the dark theme

[kswang1029]

Describe the bug
The "comment" part of the header display becomes hard to read in the dark theme as demonstrated below. We better use a lighter color to show the "comment" part.

To Reproduce
Steps to reproduce the behavior:

1. switch to the dark theme
2. use the file browser to see image header and see the issue

Expected behavior
We better use a lighter color to show the "comment" part.

Screenshots or videos
If applicable, add screenshots/videos to help explain your problem.

Platform info (please complete the following information):

• OS [e.g. macOS Monterey]: macOS Ventura
• Browser [e.g. chrome, safari, electron app]: chrome / electron app
• Browser version [e.g. 22]:
• Backend branch [e.g. dev, v3b2 release]: dev, v4.1
• Frontend branch [e.g. dev, v3b2 release]: dev, v4.1