function visible(menu_number) {
  document.getElementById(menu_number).style.visibility = "visible";
}
function invisible(menu_number) {
  document.getElementById(menu_number).style.visibility = "hidden";
}
function background1(submenu_number) {
  document.getElementById(submenu_number).style.backgroundColor = "#8c8cd2";
}
function background2(submenu_number) {
  document.getElementById(submenu_number).style.backgroundColor = "#ffbb00";
}