Group events by date

Hello! I need help with grouping events by date. I am using Event Organiser in my templates. So I am using its tags in my own PHP-templates. On this page https://arneteubel.com/kunden/rz-neu/termine/ I’d like to group my events by date. Basically I only want events that occur on the same date to be wrapped in a div so that I can address them specifically. As you can see on the page I am using a JS to find the first event of a date, add it’s date in a pink square and I am trying to make that date-square sticky so that it stays visible until the last event of that date is scrolled out of view. Like it is done here: https://schiffbauergasse.de/event

So is there any way to group events of the similar date in a wrapper?

Thank you and regards!

The page I need help with: [log in to see the link]