How do I support older Chrome, Firefox, Safari? Should I?

[asifm]

I'm not a professional web developer. I just discovered Semantic UI today. Looks like exactly what I need for my next project. There's one thing I'd like to get clarified. In the GitHub README, it says the supported browsers are:

Last 2 Versions FF, Chrome, Safari Mac

It's not clear which specific versions we are talking about here, because that would depend on when it was written.

My questions are:
How well does Semantic UI behave in older versions of these browsers that are still in use?
If not so well, should I care about this (meaning the number of users would be insignificant)?

[Jaydon]

Semantic UI seems to work nicely with older versions of browsers, the only hitch I have found so far is in the ui icon message, the text on the right spans over the icon due to a lack of flexbox support in IE. That's all I have found.

[asifm]

That's good to know. Thank you. I'm not particularly concerned about older IE. But I was a little surprised that it said it supports only the last two versions of Chrome, etc. Looks like I shouldn't worry about that either.

[gbailey]

Great thread, glad I came across this. I have clients that use ie9 still, would Semantic UI (currently at 2.2) work ok with it?