Show multiple areas and color them

Hello, I would know if It is possible shows multile area simultaneously (like Countries, Region, City,..) selected one time by name or ID like Nominatim shows.

In instance I imagine a link like https://www.openstreetmap.org/relation/45319_44915 that shows simultaneously https://www.openstreetmap.org/relation/45319 (Monza, IT) city area and https://www.openstreetmap.org/relation/44915 (Milan, IT) auto adapt the zoom and center in order to show all areas (in this sample they are 2, but could be dozens...)

And also, I will pass other parameter (the area color) like https://www.openstreetmap.org/relation/45319_44915#FF0000_00FF00 so, first area will be RED (FF0000 , RGB Hexadecimal notation) painted and the second one Green (00FF00) all with transaprent (alpha channel) = 50% in order to show behind the coloured area.