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.menu__item > a span
  {
    position: relative;
  }
  .menu__item > a span:before {
    content: "";
    position: absolute;
    width: 0;
    height: 2px;
    bottom: 0;
    left: 0;
    background-color: #b50000;
    visibility: hidden;
    transition: all 0.3s ease-in-out;
  }
  .menu__item:hover > a span:before {
  	visibility: visible;
  	width: 100%;
  }