function show_nav_menu() { document.getElementById('nav_menu_holder').className = 'visible';  }
function hide_nav_menu() { document.getElementById('nav_menu_holder').className = 'hidden';   }

function show_nav_wine() { document.getElementById('nav_wine_holder').className = 'visible';  }
function hide_nav_wine() { document.getElementById('nav_wine_holder').className = 'hidden';   }

window.onload = function () {
  if (document.getElementById('nav_menu_l') != null) {
    document.getElementById('nav_menu_l').onmouseover = function() { show_nav_menu(); }
    document.getElementById('nav_menu_l').onmouseout  = function() { hide_nav_menu(); }
    document.getElementById('nav_menu').onmouseover = function() { show_nav_menu(); }
    document.getElementById('nav_menu').onmouseout  = function() { hide_nav_menu(); }
  }

  if (document.getElementById('nav_wine_l') != null) {
    document.getElementById('nav_wine_l').onmouseover = function() { show_nav_wine(); }
    document.getElementById('nav_wine_l').onmouseout  = function() { hide_nav_wine(); }
    document.getElementById('nav_wine').onmouseover = function() { show_nav_wine(); }
    document.getElementById('nav_wine').onmouseout  = function() { hide_nav_wine(); }
  }
}