Social Media Icons hover effect (ok)

https://www.sliderrevolution.com/resources/css-link-hover-effects/

<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.6.3/css/all.css" integrity="sha384-UHRtZLI+pbxtHCWp1t77Bi1L4ZtiqrqD80Kn4Z8NTSRyMA2Fd33n5dQ8lWUE00s/" crossorigin="anonymous">

<ul>
  <li>
    <a href="#">
      <i class="fab fa-facebook-f icon"></i>    </a>
  </li>
  <li>
    <a href="#"><i class="fab fa-twitter icon"></i></a>
  </li>
  <li>
    <a href="#"><i class="fab fa-linkedin-in icon"></i></a></li>
  <li>
    <a href="#"><i class="fab fa-google-plus-g icon"></i></a></li>
</ul>
<!--
Inspired/Mocked from
How To Add Social Media Icons Without Images - Font Awesome icon css hover effect
link: https://www.youtube.com/watch?v=QaSLBMqPb2U&list=PL5e68lK9hEzePSLgrkx-PWMUjh64-BbIe
-->

body {
  margin: 0;
  padding:0;
  background: #262626;
}

ul {
  display: flex;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

ul li {
  list-style: none;
}

ul li a {
  width: 80px;
  height: 80px;
  background-color: #fff;
  text-align: center;
  line-height: 80px;
  font-size: 35px;
  margin: 0 10px;
  display: block;
  border-radius: 50%;
  position: relative;
  overflow: hidden;
  border: 3px solid #fff;
  z-index: 1;
}

ul li a .icon {
  position: relative;
  color: #262626;
  transition: .5s;
  z-index: 3;
}

ul li a:hover .icon {
  color: #fff;
  transform: rotateY(360deg);
}

ul li a:before {
  content: "";
  position: absolute;
  top: 100%;
  left: 0;
  width: 100%;
  height: 100%;
  background: #f00;
  transition: .5s;
  z-index: 2;
}

ul li a:hover:before {
  top: 0;
}

ul li:nth-child(1) a:before{
  background: #3b5999;
}

ul li:nth-child(2) a:before{
  background: #55acee;
}

ul li:nth-child(3) a:before {
  background: #0077b5;
}

ul li:nth-child(4) a:before {
  background: #dd4b39;
}