Test on one device of your choice. Open the app and set the dark mode. Add a new site and check the Loading modal has dark background and you can read the text. Navigate to the calendar tab and open the popup menu (right top). Check it has dark background and you can read the text. Navigate to private files and click on add a new file. Check the action sheet has dark background and you can read the text. Now go offline and open a new course so an alert is displayed. Check the action sheet has dark background and you can read the text. Another way to show an alert is to enable download course options on the dashboard and try to download the dev testing course.