stylesheet-injector.js

(function() {
   var css = [
      '/css/default.css',
      '/css/section.css',
      '/css/custom.css'
   ],
   i = 0,
   link = document.createElement('link');
   link.rel = 'stylesheet',
   head = document.getElementsByTagName('head')[0],
   tmp;

   for(; i < css.length; i++){
      tmp = link.cloneNode();
      tmp.href = css[i];
      head.appendChild(link);
   }
})();

Notice the semi-colon at the end of L8, oops! Comma-first FTW! Also you're appending link instead of tmp.