マウスがフィールド上を通過したときに下線CSSを実現するにはどうすればよいですか? (ナビゲーションバーコードの例)

<div class="htmleaf-container">
    <header class="header">
        <div class="wrapper">
            <h1 class="site-title">css鼠标经过出现下划线特效测试</h1>
        </div>
        <nav class="navigation">
            <div class="wrapper">
                <ul class="navigation-list ul-reset">
                    <li class="navigation-item ib">
                        <a href="#" class="navigation-link">
                            Home
                        </a>
                    </li>
                    <li class="navigation-item ib">
                        <a href="#" class="navigation-link">
                            About
                        </a>
                    </li>
                    <li class="navigation-item ib">
                        <a href="#" class="navigation-link">
                            Contact
                        </a>
                    </li>
                    <li class="navigation-item ib">
                        <a href="#" class="navigation-link">
                            FAQ
                        </a>
                    </li>
                    <li class="navigation-item ib">
                        <a href="#" class="navigation-link">
                            More
                        </a>
                    </li>
                </ul>
            </div>
        </nav>
    </header>
    <!-- /.header -->
</div>

/* defaults */
body{
   background: #494A5F;
   color: #D5D6E2;
   font-weight: 500;
   font-size: 1.05em;
   font-family: "Microsoft YaHei"," ","Segoe UI", "Lucida Grande", Helvetica, Arial,sans-serif, FreeSans, Arimo;
}
a{color: #2fa0ec;text-decoration: none;outline: none;}
a:hover,a:focus{color:#74777b;}

html,
body {
   height: 100%;
}

html {
   box-sizing: border-box;
   font-size: 16px;
}

*,
*:before,
*:after {
   box-sizing: inherit;
}

body {
   margin: 0;
   line-height: 1.5;
   font-family: Roboto, Helvectica, Arial, sans-serif;
   /*color: #333;*/
}


/* main ie fix */

main {
   display: block;
}


/* headers */

h1 {
   font-size: 2.2em;
}

h2 {
   font-size: 2em;
}

h3 {
   /*font-size: 1.8em;*/
}

h4 {
   font-size: 1.6em;
}

h5 {
   font-size: 1.4em;
}

h6 {
   font-size: 1.2em;
}


/* anchor links */

a {
   color: #009688;
}

a:hover,
a:active {
   text-decoration: none;
}


/* inline block */

.ib {
   display: -moz-inline-stack;
   display: inline-block;
   zoom: 1;
   *display: inline;
   vertical-align: top;
}


/* ul-reset */

.ul-reset {
   padding-left: 0;
   margin-top: 0;
   margin-bottom: 0;
   list-style: none;
}


/* wrapper */

.wrapper {
   width: 80%;
   margin-right: auto;
   margin-left: auto;
   padding-right: 20px;
   padding-left: 20px;
}


/* header */

.header {
   text-align: center;
}


/* navigation */

.navigation {
   background-color: #eee;
   font-weight: 700;
}

.navigation-list {
   font-size: 0;
   padding-top: 10px;
   padding-bottom: 10px;
}

.navigation-item {
   font-size: 1.2rem;
}

.navigation-link {
   display: block;
   position: relative;
   padding: 5px 20px;
   text-decoration: none;
   color: #333;
   -webkit-transition: color .2s ease-in-out;
   transition: color .2s ease-in-out;
}

.navigation-link:before {
   content: "";
   position: absolute;
   bottom: 0;
   width: 0;
   border-bottom: solid 2px;
}

.navigation-link:before {
   left: 0;
}

.navigation-link:hover {
   color: #009688;
}

.navigation-link:hover:before {
   width: 100%;
}

.navigation-link:before {
   -webkit-transition: width .2s ease-in-out;
   transition: width .2s ease-in-out;
}


/* main */

.main {
   padding-top: 20px;
   padding-bottom: 20px;
}

.content-article {
   margin-top: 80px;
}

.content-article:first-child {
   margin-top: 0;
}

.content-article > h1:first-child {
   margin-top: 0;
}
/* media queries */

@media only screen and (max-width:1024px) {
   .wrapper {
      width: 90%;
   }
}