Upload Widget: How to set a different font-size in the source labels?

revive

I guess all is in the question :-). I could not find a reference in the Cloudinary Widget API.

I tried as the following options without success:

    styles: {
      fonts: {
        default: null,
        font-size: '30px', 
        size: '30px',        
        "'Kalam', cursive": {
                url: "https://fonts.googleapis.com/css?family=Kalam",
        active: true,
        font-size: '30px', 
        size: '30px'        
      }
    }

Many thanks!