You're never supposed to use pixels in CSS anyway; you should bare minimum use percentages to account for different screen sizes to make the designs responsive and not look terrible on different screen sizes.
The new unit of measure is EM. Which is related to font size somehow. Idk, I might be outdated already. I ran screaming from front end years ago and I won't even cop to being a full stack developer these days. I'll lead full stack projects, but I'm not doing the FE dev.