.myCoolLink a {   
    color:#131D29;  
    text-decoration:none;  
    position:relative;
}
.myCoolLink a:after {  
    content: ' ';  
    height:1px; 
    width:0;  
    left:0;
    background:#131D29;  
    position:absolute;  
    bottom:-1px;  
    transition:width 0.2s ;
}
.myCoolLink a:hover:after {  
    width:100%;
}

.myWhiteLink a {   
    color:#ffffff;  
    text-decoration:none;  
    position:relative;
}
.myWhiteLink a:after {  
    content: ' ';  
    height:1px; 
    width:0;  
    left:0;
    background:#ffffff;  
    position:absolute;  
    bottom:-1px;  
    transition:width 0.2s ;
}
.myWhiteLink a:hover:after {  
    width:100%;
}