"Add a shortcut" tile in the app menu has black text

[LingMan]

Userstyle: Search
Stylus version: 1.5.1
Userstyle version: 0.7.0
Browser version: Firefox 63
Steps to reach the problem:

1. Log into your Google account.
2. Go to the Google main page.
3. Open the app menu.

Expected Behavior: Themed text "Search" on the "Add a shortcut" tile
Observed Behavior: Text still black/dark.
Note: A basically identical tile with the text "Image" is in the same place if you open the app menu on the image search page.

Relevant part of the html:
<div class="gb_qa"><div class="gb_Z gb_W" style="background-position:0 -1311px"></div><div class="gb_ra"><div class="gb_sa">Search</div><a class="gb_ta gb_gg" href="#">Add a shortcut</a></div></div>
Screenshot: