it would be quicker to use the css file the first time, and a cached copy thereafter.
i would not use a sync ajax request in the head, that can cause your page to take forever to show up on a spotty connection.
also, localStrorage can take a while to init, pausing the page while it's parsed. This is especially noticeable on portable devices. You will get faster rendering with good http caching.
(2013/5) HTML5:90.2% MOB:14% IE7:0.5% IE8:8.6% IE9:9.8% IE10:10%