Предотвращение мерцания при наведении CSS-преобразования

@keyframes spin {
  100% {
    transform: rotateX(360deg);
  }
}

ul {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}

li:hover {
  cursor: pointer;
}

a:focus,
li:hover a {
  animation: spin 0.9s 1 linear;
}

ul a {
  color: #000;
  display: inline-block;
  height: 50px;
}

ul a:focus,
ul li:hover a {
  background-image: radial-gradient(ellipse at center, #777 0%, #222 100%);
  color: #fff;
}

<ul>
  <li><a href = "admin/">Admin</a></li>
  <li><a href = "appointments/">Appointments</a></li>
  <li><a href = "blog/">Blog</a></li>
  <li><a href = "calendar/">Calendar</a></li>
  <li><a href = "contact/">Contact</a></li>
  <li><a href = "events/">Events</a></li>
  <li><a href = "forms/">Forms</a></li>
  <li><a href = "forums/">Forums</a></li>
  <li><a href = "guestbook/">Guestbook</a></li>
  <li><a href = "mail/">Mail</a></li>
  <li><a href = "members/">Members</a></li>
  <li><a href = "newsletter/">Newsletter</a></li>
  <li><a href = "notifications/">Notifications</a></li>
  <li><a href = "search/">Search</a></li>
</ul>

p a {
  color: #000;
  display: inline-block;
  height: 50px;
  z-index:0;
  position:relative;
  color:transparent;
}
p a:before {
  content:attr(data-text);
  position:absolute;
  z-index:-1;
  top:0;
  left:0;
  right:0;
  bottom:0;
  color:#000;
  transition:transform 0.9s linear;
}
p a:focus::before,
p a:hover::before {
  transform: rotateX(360deg);
  background: radial-gradient(ellipse at center, #777 0%, #222 100%);
  color: #fff;
}

<p>some content here <a href = "admin/" data-text = "Admin">Admin</a> and more here</p>