Whenever people say things like this, I can't help but go "bullshit". It's a series of information a computer follows to produce a result. That's programming whether you like it or not!
Though I really wonder how the blazes anyone could consider CSS hard... well, apart from the fact that 90%+ of the sources out there to learn from range from sleazy web-rot dirtbag scum (W3Schools for example), to having their cranium firmly wedged up 1997's rectum. Given some of the blatant disinformation, inaccuracies, and incorrect focus found online on the topic, it's not too surprising people allow themselves to be suckered into THINKING it's more difficult than it is.
Even in your smallish article you gave a few "tells" of how you've been packed full of it. Such as when you mentioned 776px, meaning you're working in a pixel mindset, meaning you're writing broken inaccessible websites that tell the target audience of EM/REM (of which I am part) to go F*** ourselves. Sounds harsh, but if you're using PX to build websites that's what you are telling large swaths of users.
I do think there are prerequisites for properly understanding CSS that people lack, such as the idea of object tree's. That's all the DOM is, an object tree, a concept so simple I picked it up as a teenager in the '80's from one chapter in a Turbo Pascal manual.
But to be fair, I've been programming for ten times longer than you, and dealing with web tech for five times as long. I started out hand coding assembly, and spent a decade working in Ada. It gives me a radically different perspective on this.
As such, I have questions for you. How are your semantic chops? Do you ACTUALLY understand what H1... H6 mean? Are you just blindly pissing classes and "Div for nothing" all over the place or are you maintaining the separation of concerns and leveraging selectors and combinators?
CSS is only as good as the HTML it is applied to, and the mind-numbingly idiotic incompetent trash we see such as the examples for and methodologies of every one of the garbage "frameworks" out there aren't doing anyone any favors.
And it's idiotic trash like that riddled with bad practices that dupe people into THINKING that vanilla HTML+CSS is "hard" when it is in fact nothing of the sort. PEOPLE make it hard by ignoring good practices, flipping the bird at accessibility, and telling the entire reason HTML and CSS exist in the first place to sod off.
Which is how all these scam artists with their frameworks and "CSS is hard" bull hoodwink and bamboozle normies with their bald faced LIES.