What are the differences between flex-basis and width?

Question

There have been questions and articles about this, but nothing conclusive as far as I can tell. The best summary I could find is

flex-basis a

Answer 1

Possibly the most important point to add:

What if the browser doesn't support flex? In such a case, width/height take over and their values apply.

It is a very good idea - almost essential - to define width/height on elements, even if you then have a completely different value for flex-basis. Remember to test by disabling display:flex and seeing what you get.