function for adding vendor prefixes
function crossBrowser(property, value, prefix) {

    function ucase(string) {
      return string.charAt(0).toUpperCase() + string.slice(1);
    }

    var vendor = ['webkit', 'moz', 'ms', 'o'],
      properties = {};

    for (var i = 0; i < vendor.length; i++) {
      if (prefix) {
        value = value.replace(prefix, '-' + vendor[i] + '-' + prefix);
      }
      properties[ucase(vendor[i]) + ucase(property)] = value;
    }
    properties[property] = value;

    return properties;
  }