Nope, sadly I can't get this to work. I've got close with this code:

#plugin-view-joplin-plugin-dddot-dddot\.panel {
  max-width: 250px !important;
  position: absolute !important;
 right: 0px!important;
}

or

.resizableLayoutItem.rli-plugin-view-joplin-plugin-dddot-dddot\.panel .sc-cwHptR.DnUmE {
 max-width: 250px !important;
 position: absolute !important;
 right: 0px!important;
}

But there is now some empty space between the editor and the plugin interface. Meaning that the plugin is stored in some sort of div that I can't quite figure out how to style?