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.
BROWSER STATS [% share]
(2013/10/31) IE7:0.5, IE8:8.6, IE9:5.3, IE10:12.3, FF:17.7, CH:41.8, SF:8.1, MOBILE:20.4