This is an experimental feature based on Apple’s StandBy mode.
STAND ASIDE mode is a CLOCK setting that try to imitate the look and feel of Apple’s StandBy mode.
To enable the feature in CLOCK:
STAND ASIDE mode only works on Google Chrome and Microsoft Edge.
It is not availble for Firefox or Safari yet.
This feature was introduced in CLOCK Version 2.1.
At this point, only the clock display dims, but more features are in development.