I imagine this is kinda hard to do with the current CSS grid implementation. You need to define where the pop-up is supposed to sit from the beginning. You can try to put it inside an additional html.Div() and make that Div a className=‘row’ perhaps.
Also was thinking that one could combine Dash with another CSS framework like bootstrap, as bootstrap provides a couple more advanced design options (including descriptions on Hover). Don’t know if anybody has tried that so far though.
EDIT: To specify further, i think you need to make a callback for the button similar to this