span a {
     position: relative;
     text-decoration: none;
     color: #000;
     transition: .5s;
     padding: 0 5px;
     ;
 }

 span a:hover {
     color: #fff;
 }

 span a::before {
     content: '';
     position: absolute;
     bottom: 0;
     left: 5%;
     width: 90%;
     height: 1px;
     background: #ff3300;
     transition: 0.5s;
     z-index: -1;
 }

 .big a:hover:before {
     left: 0;
     width: 100%;
     height: 28px;
 }

 .small a:hover:before {
     left: 0;
     width: 100%;
     height: 20px;
 }