Reply To: Header Issue in Mobile View

I’m asking for the moon and stars here. I’d love to have a custom.css file that ships with the theme, and which is pre-set to be referred to by style.css. Then in the backend interface for the theme, a Customize tab/option that opens up and allows for custom css to be added.

Here’s a screenshot of another theme that does just that:

http://screencast.com/t/OUbRVGgDK

I’m sure I can fuddle around in the files and achieve the header effect I’m looking for using custom css. But to not keep that css separate seems risky to me, as does creating custom.css on my own and trying to figure out how to make the theme refer to that custom.css file. For instance- would I then have to add something to style.css that says “let the css in custom.css overule anything in here”?

Final issue- custom.css doesn’t help at all with changes to the functions.php file. Do changes to functions.php get overwritten with a theme upgrade, too?