Best resource for proper HTML+CSS development is Jason Knight AKA deathshadow's CUTCODEDOWN (cutcodedown.com at Web archive) and his articles at Medium and CodePen (user Jason Knight).
They're not really 'tricks' as much of mentions of assorted features of HTML and CSS. You get to discover a similar assortment of things (with much more immediately available detail and many examples) just clicking around MDN.
> Each post-it pairs one useful platform feature with a small example
I can’t find a single example; each post-it just shows some code but not the result of it.
without demos this is mostly useless i think
There are some good descriptions and hints, but what the site really needs is examples. Just looking at the code doesn't help me much. The descriptions are also mostly so short, that they could just as well be tooltips on the homepage. The whole premise of the page is a collection of "web tricks worth remembering" and I can't fathom what bash (e.g. `du -hd 1 . | sort -hr`) is doing there.