This problem is making me feel like an absolute noob.
Here is the head of my .html file:
I had the same problem, and I used the UTF-8 coding for both of my files as follows:
add @charset "UTF-8"; in CSS file and under tag in HTML file.
and it worked for me.
it makes the same encoding for both the files i.e HTML and CSS.
You can also do the same for "UTF-16" encoding.
If it is still not working check for the under tag in HTML File where you should mention type="text/css"