Let's describe this feature request in Bottom Panel for example.

The user configures the height of the panel and this setting can be overriden in the current implementation.
But there are use cases that this should and must be overriden.

Example case a dock (Now Dock Panel) which zooms its content items in hovering. The ideal way  would be the panel to use the user's preference when it is not hovered but when an item is zoomed the panel increases its height. When the mouse leaves the panel, the panel restores its height.

With the current implementation unfortunately in order for the things to work the user has to set from start the maximum needed height. That has as a consequence to be used a lot of valued space from windows, desktop etc. which is not needed when the panel is not hovered...

regards, 
michail

Reproducible: Always