Another card I found when sorting through old stuff in my stamp room was a shadowbox card made a very long time ago. It inspired me to make this card using the Colorful Seasons stamp set and thinlits.
There are two pieces of card stock, each 5-1/2" x 4-1/4", and they both are scored on each end at 1/2" and 1". My back panel is Sweet Sugarplum card stock and the front panel is obviously white. The white insert is 3-1/4" x 4". The two pieces are folded and the 1/2" ends glued together. When the card is pulled from both ends it "flattens" out and will fit into an envelope. When the ends are pushed inwards it creates a shadowbox and stands up.