Mockups are mockups, they’re suggestions. More often than not, sizes and spacing don’t match across views and it’s a waste of time to be “pixel perfect.”
As I said, I don’t try to make the end result pixel perfect. I try to cut a balance between being faithful to the design and having maintainable code.
Spacing and sizes do matter though. There’s a reason why we have thousands of different fonts, even though 5 would be sufficient. When lengths are proportionate it creates positive feelings in the user. People are unconsciously very perceptive to small changes in proportions - it’s sexual attraction.
