nav
{
  text-align: center;
  clear:both;
}

#topnav {
  /* overflow: hidden;*/
  background-color: #333;
  width:100%;
}

#topnav a {

  margin: auto;
  display: inline-block;
  color: #f2f2f2;
  text-align: center;
  padding: 10px 16px;
  text-decoration: none;
  font-size: 17px;
}

.sticky
{
  position: fixed;
  top: 0;
}

.sticky + .content {
  padding-top: 60px;
}
#topnav a:hover {
  background-color: #ddd;
  color: black;
}

#topnav a.active {
  background-color: red;
  color: white;
}

#topnav .icon {
  display: none;
}

@media screen and (max-width: 400px) {
  #topnav a:not(:first-child) {display: none;}
  #topnav a.icon {
    float: right;
    display: block;
  }
}

@media screen and (max-width: 400px) {
  #topnav.responsive {position: relative;}
  #topnav.responsive .icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  #topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
}

input:required:invalid, input:focus:invalid {
  /* insert your own styles for invalid form input */
  color: red;
}