Base: Score 12" x 12" CS at 5" and 7". In the other direction, score at 3" and 9", the cut sides at score lines into the 5 & 7 score lines. Fold these flaps into the center and glue down (for extra support). This is the bottom of your box. Cut 1-3/4" off each side of the top panels only. Score the bottom flaps 1" in from each side.
Box Lid: Score a 8-1/2" x 4-1/4" CS at 1-1/4" on all four sides. Embellish as you desire.
Card Holder: Score a 8-1/2" x 4-1/4" CS at 1-1/4" on both short sides and one long side. Trim corners and apply glue or sticky strip to scored sections. Fold up the top of the card box and attach to the two sides that were cut and the bottom.