Crossbrowsing, flexobox, bootstrap?

Question

css

What cross-browsing is relevant now? What technologies to use and libraries?
Right now, I'm only building for sites with the latest version on flexbox/bootstrp 4.
What technologies should I use for, say, IE 9 versions, etc.?

Answer 1

Here is a site where you can look where there is support

Answer 2

What technologies is used for, say, IE 9 version and so on?

You can try the "Drive in a bolt" technology, many advise, it has been working for me without fail for almost a year.
But seriously: use the technologies that are supported there, that's all, you can check it through caniuse.com, for example.

Answer 3

float is eternal xD

Answer 4

Since this year, they have refused to support IE in general based on visit statistics (<1%). Corporate sites and industrial portals.