text/css header 

In Chrome console I get:
Resource interpreted as Stylesheet but transferred with MIME type text/html: "http://localhost/moodle26/blocks/accessibility/userstyles.php". 

Fixed according to:
http://stackoverflow.com/questions/5413107/headercontent-type-text-css-is-working-in-ff-cr-but-in-ie9-it-shows-up-as