Thanks to the upgraded monarch, I was able to make sliding windows.

...
But the following problem has come to light - the windows slide unevenly.
You can see it in the video if you look closely.
This can also be seen in the screenshots:

Apparently, for some windows, the transition is triggered a couple of frames later.
This could be remedied by passing some sort of start time to all transitions, and compensating the delay via a negative delay in the gui.animation().