I recently got interest into web dev and... why isn't HTML + CSS considered art? I keep moving stuff one px to the left, one to the right then back left padding-top :40px, ehh to much, 20px ehh too little 30px ehh lemme just leave it at 40px. It's like when you erase a line on a drawing.

Design is definitely an art. If you are designing while making CSS, I'd argue that is just a coincidence; indeed, often, a design is made beforehand using Illustrator or other design software and you build CSS+HTML off of that.

Theres still an art to designing good stylesheets, but it's a distinct art :)