how to open a block in a popup window like twitter?

I would like to have a button that floats on the bottom of the site, and when someone clicks it the create post block opens. This way they won't be redirected after making video and module posts and also it will make it easier for them to quickly post while browsing the site. When they finish posting, the popup closes.

Also, I want to make one for messenger too. So the messenger is accessible everywhere.

The create posts button will be a feather and the messenger button will be a chat icon.