* {
  margin: 0;
  padding: 0;
}
body {
}

div#wrapper {
}
  div#header {
  }
  div#content {
  }
  div#footer {
  }
  
div#nav {
  margin:0 auto;
  width:400px;
  height:400px;
  background:green;
    position:relative;
}
  div#nav li {
    width:100px;
    height:50px;
    display:block;
    float:left;
    background:red;
  }
  div#nav div#submenus {
    height:300px;
    width:400px;
    margin-top:50px;
  }
    div#navigation div.submenu {
      display:none;
      position:absolute;
      left:0px;
      top:50px;
      height:300px;
      width:400px;
      background:gray;
    }