Why we use snällt insted of snäll here?
As I am a native speaker it hard to give a detailed answer but it has to do with the fact that vänligt is in front of snäll. When I look at the whole sentence “Det är inte väldigt snällt av dig”, one thing that sticks out is that there is the word dig.
Which is the accusative/dative form of du. So it leads me to believe that it has to do with the fact that vänligt snällt are “conjugated” since they refer to dig which would be in the accusative form.
ok I will try to remember these two words together… Vänligt snällt