I started by swiping some white ink on the craft cardstock with a sponge. Let it dry for a few minutes/seconds then stamped the box with black craft ink just to be sure it would show up well. While it was drying I stamped the heart in Melon Mambo and cut it out then added 2 dimensionals stacked to really give it some pop. The sentiment piece is made with Fancy Flexible Phrases (still one of my faves even though it is long retired!!) and I just cut it out by hand then notched the ends with the 1/4" square punch- easy! It is on a tiny bit cut from dimensionals as well (I do this all the time- cut them into little pieces).
Inside I stamped hearts multiple times with Melon Mambo and white then popped one out on a thin strip of kraft cardstock that was just folded accordion style. It's simple, but adds some fun when it pops out at the person opening the card for a little surprise.
I hope you like it and you try to pop something out yourself! It's fun and easy!
Stamps: Out of the Box, Fancy Flexible Phrases (retired)
Colors: Kraft, Basic Black, Melon Mambo, Whisper White
Accessories: Stampin' Dimensionals, sponge