function toggle_visibility(id) {
       var e = document.getElementById(id);
       if(e.style.display == 'block')
          e.style.display = 'none';
       else
          e.style.display = 'block';
    }

function updateStyleSheet(filename) {
 
    newstylesheet = "css/style_" + filename + ".css";
    if ($("#dynamic_css").length == 0) {
        $("head").append("<link>")
        css = $("head").children(":last");
        css.attr({
          id: "dynamic_css",
          rel:  "stylesheet",
          type: "text/css",
          href: newstylesheet
        });
    } else {
        $("#dynamic_css").attr("href",newstylesheet);
    }
 
}