It absolutely has breaking changes! But most developers will never notice. I work on a complex browser based web development platform and we’ve had certain specs change under our feet leading to incidents that required us to disable features until major browser vendors reverted things. I do not envy spec authors. Huge respect for their patience.

I didn’t interpret it as a break in compatibility, more so that simply because a new feature or addition in CSS arises it doesn’t stipulate that you have to adopt it. You can still continue on writing CSS how you want to. I appreciate that it makes it more difficult when new features come about in a language and you have to work on a shared codebase, you sometimes spend a while looking at many differing ways to achieve the same result.