title: How to add a custom button inside Google Calendar?
body: <p><a href="https://i.stack.imgur.com/5MWQC.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5MWQC.png" alt="I want to have custom button as shown in the image"></a></p>
  
  <p>Is it possible to have the feature in the image  inside Google Calendar. I came across Gadget in Google Calendar,  but I cannot figure out how to do it. Is there any way Google is allowing to add add-ons for calendar?</p>