@charset "utf-8";
#nav_home, #nav_alertbox, #nav_lecture, #nav_whatis, #nav_about {
    position: absolute; 
}

#nav_home          { width: 70px; margin-left: 0px; }
#nav_home a        { width: 70px; background-position: 0px   0px; }
#nav_home .current {               background-position: 0px -40px; }
#nav_home a:hover  {               background-position: 0px -80px; }

#nav_alertbox          { width: 190px; margin-left: 70px; }
#nav_alertbox a        { width: 190px; background-position: -70px   0px; }
#nav_alertbox .current {               background-position: -70px -40px; }
#nav_alertbox a:hover  {               background-position: -70px -80px; }

#nav_lecture          { width: 190px; margin-left: 260px; }
#nav_lecture a        { width: 190px; background-position: -260px   0px; }
#nav_lecture .current {               background-position: -260px -40px; }
#nav_lecture a:hover  {               background-position: -260px -80px; }

#nav_whatis          { width: 150px; margin-left: 450px; }
#nav_whatis a        { width: 150px; background-position: -450px   0px; }
#nav_whatis .current {               background-position: -450px -40px; }
#nav_whatis a:hover  {               background-position: -450px -80px; }

#nav_about          { width: 130px; margin-left: 600px; }
#nav_about a        { width: 130px; background-position: -600px   0px; }
#nav_about .current {               background-position: -600px -40px; }
#nav_about a:hover  {               background-position: -600px -80px; }