Kim Kardashian stole the show as she arrived at her sister Kourtney Kardashian's eldest son Mason Disick's epic 13th birthday bash in Los Angeles on Saturday night.The SKKN founder, 42, flaunted her shrinking waistline in a pair of black leather high-waisted pants covered in sparkly black jewels.She styled the eye-catching trousers with an ultra cropped Up in Smoke Tour tee that stopped just below her bust. Scene stealer: Kim Kardashian stole the show as she arrived at her sister Kourtney Kardashian's eldest son Mason Disick's epic 13th birthday bash in Los Angeles on Saturday nightKim's pants came with a matching pint-sized purse that was not large enough to hold her cellphone.She accessorized with a flashy diamond choker necklace, as well as a silver cross pendant chain.