Article continues below advertisementDemi Lovato lit up Instagram with a fresh batch of vacation photos, showing off a confident glow while rocking a sleek black-and-white bikini.Article continues below advertisementThe 33-year-old superstar posed on the deck of a boat, smiling in the sun as she modeled a retro two-tone swimsuit with a structured top and high-waisted bottoms finished with a bold belt detail. The "Heart Attack" singer kept the look clean and cool, wearing dark sunglasses and slicked-back hair while the ocean shimmered behind her.