.img-fluid.align-content-center.img-responsive {
  max-width:25%;
}

.centered {
  float:none;
  margin-left:0;
  margin-right:0;
}

.navbar-nav {
  display:-ms-flexbox;
  display:flex;
  -ms-flex-direction:column;
  flex-direction:column;
  padding-left:0;
  margin-bottom:0;
  list-style:none;
  color:yellow;
}

.dropdown > a:hover {
  color:#ffff00;
}