The idea of a responsive pixel is solid. However, the way you’re doing things has a few problems.

1. Safari doesn’t support calc(px + vw)
2. Your repsonsive pixel doesn’t equal to one pixel at every breakpoint

Check out this article I wrote to have a clearer grasp of the calculations: http://zellwk.com/blog/viewport-based-typography/

Hoping to see more awesome work + changes from you!