There is a certain style im trying to achieve with my singing. Something similar to Mark Hoppus (Blink 182, +44)

Is his singing pure "chest" or mix? And how would I go about developing the same style. NOT as in sounding like him.
Well, I haven't listened to any Mark Hoppus so I wouldn't know. You should research on the average range of chest voice and head voice. I think you know that a "mixed" voice is between the ranges of the chest and head voice, with the thyroartenoids and the cricothyroids sharing muscle function. No person just has one placement range.

Of course, Hoppus's lower notes wouldn't be in the mixed voice unless his voice is naturally a bit higher like Etienne Sin or Vic Fuentes. And developing the same style as Hoppus (or anybody) really doesn't involve any more than singing techniques (such as vibrato, strain, belting, fry, and other embellishments) and vocal placement (chest, mix, cranial, nasal, oral) together

hope this helped!