I have seen many souce codes but I have never ever come across a code which imports any css file within a div. W3C allows it,
Importing a style sheet to apply as a scoped style sheet:
<div class="navigation" style="@import url(navigationstyles.css);">...</div>
Why do people still not use it?
That document you link to is a 10-year-old draft, and far from the latest. Now, if you look at the latest revision of the Style Attributes spec, which is a 2010 Candidate Recommendation that covers basically the same inline style declarations that we use every day, you won’t find any
@importrules mentioned anywhere anymore.This means they took it out, presumably because it didn’t make sense in retrospect, or it was difficult to implement, or some other reason entirely.