It's Dare 2B Artzy's Slim Retro Background, of course; just one of many fine Dare 2B Artzy Die Sets that can be found at The Ink Pad!
These dies would work beautifully with found or vintage papers; stamped, stenciled or gel-printed backgrounds; and just imagine how fun of a shaker card you could make? In addition to the fab and funky slimline sized background panel, there's a surrounding stitched frame die as well as nine tiny accessory dies that includes circles, squares, stars, hearts and birthday candles, plus that fun "Hi!" sentiment. I cut a bunch of layers from Craft Consortium's gorgeous Dark Tone Grunge Papers, then had fun mixing and matching different colors to make the most dynamic design. I used a black brush pen to ink the interior edges (from the reverse side of the paper!) to make the shapes stand out more, and mounted the panel with the cut-outs on a layer of double-stick foam tape.