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/* Demo http://www.gleenk.com/demo/css/hover-effects-css3/# */
  .link-testo {
    display: inline-block;
    position: relative;
    text-decoration: none;
  }
  .effetto-testo {
    &:hover::before {
      width: 100%;
    }
    &:before {
      background: #fff none repeat scroll 0 0;
      bottom: 15px;
      content: " ";
      display: block;
      height: 2px;
      position: absolute;
      transition: width 0.2s linear 0s;
      width: 0;
    }
  }

<a href="#" class="link-testo effetto-testo">
<h4>Demo1</h4>
</a>