Notification count color lacks contrast

The notification span has a pure red (#ff0000) background, whatever the colortheme.

The white text (count of notifications) constitutes a WCAG violation with a contrast of 3.35 <4.5 minimal contrast for WCAG 2.1 AA.

This background needs to be darkened, or the text swapped to a dark color instead.

Moreover, the color of this background is hardcoded, and should use a color theme variable instead.