Creating a custom app that operates similar to the ellipses button on the vertical taskbar.

Hi all, 

Trying to create a app for Microsoft Teams that would operate the same way the ellipses button can operate on the vertical taskbar. Once clicked it would open a small popup/dialogue box with some content without opening a new personal app window.

For example, if the user were on the files screen, if they clicked this custom app, the custom app would have a small popup/dialogue box overlayed on top of the files screen. 

Just want to know if it is possible?

Thanks!