Clean underline link:hover transition (smooth underline width from 50% to 100%)

link_hover.css

/* You're welcome. */  
  a {
    text-decoration: none;
    position: relative;
    overflow: hidden;
  }
  a:hover {
    text-decoration: none;
  }

  a:after {
    background-color: #fff;
    bottom: -9px;
    content: "";
    height: 2px;
    position: absolute;
    width: 0;
    left: 50%;
    max-width: 100%;
    -moz-transform: translateX(-50%);
    -ms-transform: translateX(-50%);
    -webkit-transform: translateX(-50%);
    transform: translateX(-50%);
    -webkit-transition: width .1s;
    -o-transition: width .1s;
    transition: width .1s;
  }
  a:hover:after {
    -webkit-transition: width .1s;
    -o-transition: width .1s;
    transition: width .1s;
    width: 100%;
  }