Here's the basic box:
Start with a piece of 11 1/2 x 12 cardstock (bottom) and a piece that is 7 x 5 (lid). Here I used green for the bottom and Merry Wishes for the lid.
Score the 11 1/2 x 12 piece at 2 1/2" from each edge on the 12" side and 4 1/2" from the edges on the 11 1/2" side.
With the 7x5 piece portrait style, score the paper at 1" from one edge and 1 1/2" from the other side.
Looking at your box bottom, you will see two small squares formed by the score lines. Cut on the score lines that form the sides of the squares to make tabs.
Fold the box bottom on all score lines and adhere the side flaps together with strong adhesive.
Fold the box lid on the two score lines. Place wonder tape on the 1" flap and press that onto the back of the box. Use a corner rounder on the corners of the lid. Set an eyelet in the center of the lid's front flap. Run two pieces of ribbon through the eyelet and tie in a knot behind the eyelet to secure. Wrap the ribbon around the box and tie in a bow to secure.
This box will hold at least 12 A2 sized cards and envelopes.