var style_cookie_name = "style" ;
var style_cookie_duration = 30 ;

function switch_style ( css_title ) {
  var i, link_tag ;
  for (i = 0, link_tag = document.getElementsByTagName("link") ;
    i < link_tag.length ; i++ ) {
    if ((link_tag[i].rel.indexOf( "stylesheet" ) != -1) &&
      link_tag[i].title) {
      link_tag[i].disabled = true ;
      if (link_tag[i].title == css_title) {
        link_tag[i].disabled = false ;
      }
    }
    set_cookie( style_cookie_name, css_title, style_cookie_duration );
  }
}
function set_style_from_cookie() {
  var css_title = get_cookie( style_cookie_name );
  if (css_title.length) {
    switch_style( css_title );
  }
}
function set_cookie ( cookie_name, cookie_value, lifespan_in_days, valid_domain ) {
    var domain_string = valid_domain ? ("; domain=" + valid_domain) : '' ;
    document.cookie = cookie_name + "=" + encodeURIComponent( cookie_value ) + "; max-age=" + 60 * 60 * 24 * lifespan_in_days + "; path=/" + domain_string ;
}
function get_cookie ( cookie_name ){
    var cookie_string = document.cookie ;
    if (cookie_string.length != 0) {
        var cookie_value = cookie_string.match ('(^|;)[\s]*' + cookie_name + '=([^;]*)' );
        return decodeURIComponent ( cookie_value[2] ) ;
    }
    return '' ;
}