灵动的动画 TAB 切换效果

.m { margin: 100px; }

.tab { width: 400px; margin: 0 auto; border: 1px solid #ddd; height: 40px; text-align: center; line-height: 40px; background: #fff; border-radius: 10px; overflow: hidden; }
.tab li { float: left; width: 100px; position: relative; overflow: hidden; }
.tab li:before, .tab li:after, .tab li a { -webkit-transition: all 0.25s ease-in-out; transition: all 0.25s ease-in-out; }
.tab li:before, .tab li:after { content: ""; display: block; }
.tab li:not(:first-child):after { background: #ddd; height: 20px; width: 1px; left: 0; top: 10px; position: absolute; }
.tab li a { display: block; position: relative; z-index: 2; color: #000; font-size: 14px; }
.tab li:before { width: 0; height: 0; top: 50%; left: 50%; z-index: 1; position: absolute; }
.tab li:hover a { color: #fff; }
.tab li:hover:before { box-shadow: 0 0 0 100px #36bc99; }
.tab li:hover + li:after, .tab li:hover:after { height: 0; top: 20px; }

 <div class="m">
    <ul class="tab">
      <li><a href="">导航1</a></li>
      <li><a href="">导航2</a></li>
      <li><a href="">导航3</a></li>
      <li><a href="">导航4</a></li>
    </ul>
  </div>