These definitely could be worn casually with just runners and a Tshirt, or could be dressed up with wedges and a dressy top. They are so comfortable.
Sizing and fit: There is plenty room for manoeuvre is the sizing of these. The S will fit sizes 8 to 12, the M will fit sizes 12 to 16, and the L will fit from 14 to an 18. Elasticated waist with plenty room in the legs too.