.header ul li {
display: inline;
}
.header ul a {
display: inline-block;
overflow: hidden;
white-space: nowrap;
width: 30px;
-webkit-transition: color .25s ease-in-out, width .25s ease-in-out;
-moz-transition: color .25s ease-in-out, width .25s ease-in-out;
-ms-transition: color .25s ease-in-out, width .25s ease-in-out;
-o-transition: color .25s ease-in-out, width .25s ease-in-out;
transition: color .25s ease-in-out, width .25s ease-in-out;
}
.header ul a.active, .header ul a:hover {
width: 150px;
}
.header .fa{ width:30px;}
</style>
html 部分
<div class="header"><ul>
<li><a href="#"><i class="fa fa-anchor"></i><span>投資組合</span></a></li>
<li><a href="#"><i class="fa fa-bell-o"></i><span>下午7時26分</span></a></li>
<li><a href="#"><i class="fa fa-taxi"></i><span>日出</span></a></li>
<li><a href="#"><i class="fa fa-cogs"></i><span>背景</span></a></li>
</ul>
</div>