I think a _lot_ of this is standardised now in the vast majority of browsers people use.

Depending on what space you work in and what consumers you have “majority” is not acceptable.

Safari and IE are the big bugbears in my experience.

True - I'm lucky not to have to consider versions of IE prior to 11 on most projects I work on, and I can usually get things working there, although there's a flexbox thing that I always forget with IE11 that catches me out.

I stand by my comment if you don't have to do IE < 11 though.

Even just IE11 is pretty bad given the state of grid and flexbox on IE11.

Yeah, grid is pretty much not worth it imo, as you have to do so much differently. You can make flexbox work though.

The environment for CSS isn't nearly as "standard" as you might think. Even though WebKit and Blink are the majority engines on mobile there's tons of combinations of versions, screen sizes, and aspect ratios. Trivial layouts are easy but more complicated layouts can be very difficult to get working right, let alone looking right, across browsers/platforms.

The problems are often solvable but not necessarily easy. The difficulty is compounded by the heterogeneity of the Android space.

It's great the majority browser engines follow the CSS standards but a lot of problems aren't bounded by the accuracy of the implementation.

Without wanting to diminish what you're saying, which makes a lot of sense - I feel like we should be trying to avoid complex layouts on mobile - at least in the browser.

And you're right that screen sizes can mess stuff up, Firefox/chrome mobile view on devtools doesn't always tell the full story... Got something working there and it was broken on my actual phone.