Night Eye can offer more than simply dark UI.
There are many customisation options such as blue light filter, contrast filter, brightness filter, color changing feature and more. For most people, the default settings are satisfactory enough so at the beginning don’t bother with them. Night Eye will automatically enable dark mode on every website you visit.
Does this work on the Google Calendar mobile apps (iOS and Android)?
Sadly, but no. Night Eye is available only for the web version of Google Calendar. For the mobile apps we hope that at some point Google will implement dark mode throughout their whole range of apps.
Google Calendar guide - from beginner to expert
Comprehensive and easy to digest guide on how to become Google Calendar master - https://www.calendar.com/google-calendar-guide/