R – Hosting YUI in SSL Site – IE Errors

I'm using YUI on my site. It works fine with no errors when you access over HTTP. However, when IE users access the site over HTTPS they get the dreaded "this page contains secure and nonsecure items" error message, which makes it really close to unusable.

I'm hosting the YUI files, so they're getting served up over HTTPS, but in the CSS file, it's referencing an image file over HTTP still which causes the IE error message to appear:

background:url(http://yui.yahooapis.com/2.7.0/build/assets/skins/sam/sprite.png)

Any suggestions for suppressing this error? There are a ton of HTTP links referenced in the CSS.