In python, I can read code and reason about what it will do because I have a mental model of how that language works. the same used to be true of C and probably still is, but I'm out of practice.
I've been trying to build a coherent mental model of how layout in HTML+CSS works since 2008 and still haven't really been able to. If you gave me an html file and CSS file, I'm not at all confident I could draw they would interact. Conversely, if you showed me an HTML page, I don't think I could write HTML and CSS to reproduce it without continually refreshing my browser to check it. I have been trying to determine why I can't seem to learn this.
It's a visual thing. Frontend isn't very similar to programming for the backend (except for high quality javascript). Most people who can do wonders for frontend tend to be more like designers.
Ugh. Before the advent of CSS3 and canvas, I would have rated myself an 8 out of 10 in terms of "frontend knowledge/skills" compared to other frontend developers I'd met. I was never the cream of the crop (as a backend "expert"), but I could take a photoshop and replicate it, and knew most of the browser compatibility issues and how to work around them.
With all the CSS transforms, animations, canvas, 3d libraries, etc., I'm now utterly lost. I've gone from being an intermediate frontend guy to a 6/10 on the core necessities (all that earlier knowledge is still the foundation), but like a 1/10 or 2/10 with all the new stuff. I could probably get to 4/10 if I put in the effort, but I have a very strong gut feeling that I simply do not have the... faculties... required to be an intermediate frontend guy in 2015.
All that to say... codepens like these I've seen blow me away. I don't even bother trying to dig into the CSS. It's just beyond me. ;)
I've been trying to build a coherent mental model of how layout in HTML+CSS works since 2008 and still haven't really been able to. If you gave me an html file and CSS file, I'm not at all confident I could draw they would interact. Conversely, if you showed me an HTML page, I don't think I could write HTML and CSS to reproduce it without continually refreshing my browser to check it. I have been trying to determine why I can't seem to learn this.