test.css

a{
  position: relative;
  display:inline-block;
  padding: 15px 30px;
  color: #2196f3;
  letter-spacing: 4px;
  text-decoration: none;
  font-size: 24px;
  overflow: hidden;
  transition: 0.2s;
}

a:hover{
  color: #255784;
  background: #2196f3;
  box-shadow: 0 0 10px #2196f3, 0 0 40px #2196f3, 0 0 80px #2196f3;
  transition-delay: 0.6s;
}

nav ul li a span{
  position: absolute;
  display: block;
}
nav ul li a span:nth-child(1){
  top: 0;
  left: -100%;
  width: 100%;
  height: 2px;
  background:linear-gradient(270deg, transparent, #2196f3);
}

nav ul li a:hover span:nth-child(1){
  left:100%;
  transition:0.5s;
}

nav ul li a span:nth-child(3){
  bottom: 0;
  right: -100%;
  width: 100%;
  height: 2px;
  background:linear-gradient(270deg, transparent, #2196f3);
}

nav ul li a:hover span:nth-child(3){
  right:100%;
  transition:0.5s;
}