Unread circles not visible enough

Benoît and Marjolaine reported unread circles were not visible enough. I agree with them.

Turning the font color to white seems to solve the problem for them:

A short comparison with Slack to illustrate the problem: https://imgur.com/a/EiC66p5

changed time estimate to 45m

assigned to @jbpasquier

mentioned in merge request !196 (merged)

closed via merge request !196 (merged)