[cud] navbar li hover effect

header li a {
  position: relative;
}
header li:not(.selected) a:after {
  transition: height 1s;
  position: absolute;
  content: "";
  display: block;
  background: #f8f8f8;
  border: 1px solid #E6E8EB;
  width: 40px;
  border-bottom-color : #f8f8f8;
  bottom: -2px;
  left: calc(50% - 20px);
}
header li:not(.selected):hover a:after {
  height: 6px;
  bottom: -1px;
}