CSS EM测量混乱?

我的em单位有问题,我将导航列表宽度设置为6.250em,相当于100px,工作正常。当我将每个li的宽度更改为6.250em时,它不会延伸到与导航列表相同的宽度。为什么会发生这种情况,我该如何解决?

CSS代码:

.navlist {
  width: 100px;
  height: auto;
  float: left;
  margin: 0;
  padding: 0;
  list-style-type: none;
  background-color: #000; 
}
.navlist li {
  font-weight: bold;
  font-family: sans-serif;
  font-size: 14px;
  text-align: center;
  text-transform: uppercase;
  text-shadow:0px 1px #14161A; 
}
i {
  font-size: 26px;
  padding-bottom: 6px;
}
a.nav-buttons {
  width: 6.250em;
  height: 60px;
  display: block;
  display: table-cell;
  vertical-align: middle;
  color: #CCC;
  text-decoration: none;
  background-color: #666;
  border-top: 1px solid #2E3139;
  border-bottom: 1px solid #14161A; 
}
a.nav-buttons:hover, a.nav-buttons:focus {
  color: #fff;
}

HTML代码:

<ul class="navlist">
    <li><a href="#" class="nav-buttons"><i class="fa fa-home"></i> Home</a></li>
    <li><a href="#" class="nav-buttons"><i class="fa fa-info-circle"></i> About</a></li>
</ul>

JSFiddle此处: http://jsfiddle.net/2ZT9w/1/