its probably a cache issue, just delete all browsing data, history, cache, 
cookies, e.t.c and then close the browser and open again, it should fix the
problem as it fixed mine.

But the best way to actually fix this problem is by calling the css file with
php. i recommend calling your css stylesheet with php because, if your website
is online , you cant tell all your users to delete their browsing data every
  time you apply a change on the website

its very simple, first you write the style tag then call the css file with php.