I've spent a lot of time in the past year mucking with CSS, some my own, but most of it applying to other sites via browser extensions. I'd learned most of the specific spec entities described here (though learned a few terms I'd not picked out before), some of which have proven quite useful in getting the results I want. Which often translate to "make the goddamned page readable".
And yes, I restyled the referenced page to improve readability (text to white, larger fonts, different spacing and padding).
You'll likely only need this "true understanding" if you're editing said specification. Or implementing it.