This looks like a bug to me since I can clearly differentiate between today's date (Dec 13)as well as assigned date(Dec 23) to a topic in Light Mode.
I will forward this information to the testing team to open as a defect.
Thanks for providing the feedback.
After discussing with my engineering team I came to know that we are using standard controls from macOS to launch scheduler.
Following screen shot has example of showing the display inside Calendar app as well as MindManager application.