Cotton Floral

What kind of wedding is this?!?!?

I am attending a wedding in a week… and am confused if this wedding is supposed to be formal or informal attire. The invitation says nothing about attire or if it’s an adult only reception.
The wedding is on a Friday, but the cermony starts at 6pm.
The invitation is embossed, but the address is handwritten in print
The cermony and reception are in the same place.
I am wearing a dress, but I am worried about being underdressed or overdressed… do I wear a bright floral cotton spring dress? Or do I wear a black silk dress? I have never been to a wedding in which I have been so unclear on what to wear.

Since it is evening, I would stay on the dressier side. The black silk sounds more appropriate than the cotton dress.

H by Heidi Weisel Sateen Cotton Floral Skirt