fix: category dropdown

[huyenltnguyen]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Fixes a couple of issues in the Category dropdown:

• The dropdown color is lighter than the rest of the buttons.
  • 
• Dropdown items text doesn't have sufficient contrast against the background.
  • 

Results

Screenshots

At rest

Theme	Screenshot
Day
Dawn
Night

Expanded and hovered

Theme	Screenshot
Day
Dawn
Night

[huyenltnguyen]

This is my code from a previous PR. I figured using a background color token for text color is weird, so I changed it to primary-low.

This is essentially a change in the gray scale and slightly increases the contrast of the text against the background.

[huyenltnguyen]

This is to correct the text color when the dropdown button is at rest.