How can I make this 1x1 spacer invisible?

[hotNipi]

As you are already overriding dashboard default styles, add this rule

ui-card-panel:has(.invisible-group){
   opacity:0 !important;
}

And for that ui_teplate node which is situated in the group which becomes invisible give a class "invisible-group"

[Loveflowersx]

It worked, thank you very much!!!