https://caniuse.com/#search=flexbox https://caniuse.com/#search=grid
It's almost like an uncanny valley effect - its similar enough to lure you into a false sense of security, until you realise that defaults for flex-direction are reverse, or it implements flex/flex-grow/flex-shrink/flex-basis completely differently.
I would guess this probably started off as an unofficial endeavour by a single or small group of employees and the beancounters agreed to publish it as OSS.
http://carbondesignsystem.com/ https://github.com/carbon-design-system/carbon-components-re...
I'd like it to be the former, so that I can be productive out of the gate and figure out what I'm doing as I go. That may be unprofessional, but I make quick-and-dirty prototypes for academics; nothing that has to scale. Plus, I'm lazy.
This tool seems oriented at abstracting away a lot of detail, and to be aimed at solutions that have to scale. If I wanted to learn as I go, I'd start without the abstractions.
I had a bunch of my colleagues work through http://cssgridgarden.com/, which seemed to be a good first start for them. There are tons of other resources out there, so it depends what you're after.