CSSRule is a constructor that allows to create classes on the run, it detects the prefix needed and you can use it by sending a callback function instead of a string to the add method.

css.js

var CSSRule = (function (){
  var prefix = (function getPropertiesPrefix(){
    var t, el = document.createElement("fakeelement")
    ,animations = {
      "animation": "",
      "OAnimation": "-o-",
      "msAnimation": "-ms-",
      "MozAnimation": "-moz-",
      "WebkitAnimation": "-webkit-"
    };
    for(t in animations) if(el.style[t] !== undefined){
      return animations[t];
    }
  })();
  function CSSRule(name){
    this.name = name.trim();
    this.rules = {};
  }
  Object.defineProperties(CSSRule.prototype, {
    'add': {
      value: function (prop, val){
        if(typeof prop === 'function'){
          prop.call(null, prefix, this.rules);
        } else this.rules[prop] = val;
        return this;
      }
    }
    ,'create': {
      value: function (){
        var rule = this.name + ' { ';
        for(var prop in this.rules) if(this.rules.hasOwnProperty(prop)) {
          rule += prop + ': ' + this.rules[prop] + ';';
        }
        rule += ' }';
        if( document.styleSheets && document.styleSheets.length ) {
          document.styleSheets[0].insertRule(rule, 0);
        } else {
          var s = document.createElement( 'style' );
          s.innerHTML = rule;
          document.head.appendChild(s);
        }
        return null; // we return null because once created, we don't need to change it
      }
    }
  });
  return CSSRule;
})();