Learn it bit by bit as you actually need it.

If you make stuff capable of graceful degradation (eg for older browsers) then you can give yourself some space and time for graceful and incremental CSS upgrades!

My CSS vocab is still I think very small (and I've a couple of big chunks coming that I want to understand) but it can be used like a scalpel: tiny uses of it can do good things.

I've been writing HTML since it was a thing (90s).

Boring is a matter of perspective I guess. I find coding out API endpoints, configuring infrastructure, and building database schema to be excruciatingly boring. But building a UI in the browser and watching it come together is extremely satisfying. Gaining a solid expertise with CSS is table stakes for a web developer IMO. You can raise your nose at it and say "that's not real programming so I don't care", but it's ultimately a part of the whole package and not being able to do it makes you weaker as a developer. You should be able to look at absolutely any design and recreate it perfectly.

You can try this site: https://cssbattle.dev/

You try to match the source image using css.

You can even find youtubers who compete. I find it pretty entertaining. It helped me get from being afraid of writing styles to enjoying it.

There are lots of things on the web that gamify aspects of css: FlexBox Froggies comes to mind.

I don't really see it as boring to begin with honestly. I like building UIs, so I don't think it's boring to learn to build UIs.