Formatting/font size

I’m copying and pasting from a cloud-based word processor (StoryShop) into Scriv and I can’t figure out the formatting, specifically the font size. SS only has S, M, L font sizes. When I copy and paste (one chapter at a time) the font size in Scriv says (-1). And I can’t for the life of me figure out how to change it. Every time I try, as soon as I put the cursor in the text field, it pops back to -1. Please help!!!

Try using ‘Paste and Match Style’ instead of Paste