导航栏100％宽度居中

我已经尝试了一段时间，以使导航栏中的所有内容居中。这是我的CSS和HTML代码，如果有人可以给我提示该怎么做，我将不胜感激。

#cssmenu ul {
  margin: 0;
  padding: 0;
}


#cssmenu li {
  margin: 0;
  padding: 0;
}
#cssmenu a {
  margin: 0;
  padding: 0;
}
#cssmenu ul {
  list-style: none;
}
#cssmenu a {
  text-decoration: none;
}
#cssmenu {
  height: 70px;
  background-color: #232323;
  box-shadow: 0px 2px 3px rgba(0, 0, 0, 0.4);
  width: auto;
  text-align: center;
}
#cssmenu > ul > li {
  float: left;
  margin-left: 15px;
  position: relative;
}
#cssmenu > ul > li > a {
  color: #a0a0a0;
  font-family: Verdana, 'Lucida Grande';
  font-size: 15px;
  line-height: 70px;
  padding: 15px 20px;
  -webkit-transition: color .15s;
  -moz-transition: color .15s;
  -o-transition: color .15s;
  transition: color .15s;
}
#cssmenu > ul > li > a:hover {
  color: #ffffff;
}
#cssmenu > ul > li > ul {
  opacity: 0;
  visibility: hidden;
  padding: 16px 0 20px 0;
  background-color: #fafafa;
  text-align: left;
  position: absolute;
  top: 55px;
  left: 50%;
  margin-left: -90px;
  width: 180px;
  -webkit-transition: all .3s .1s;
  -moz-transition: all .3s .1s;
  -o-transition: all .3s .1s;
  transition: all .3s .1s;
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;
  border-radius: 5px;
  -webkit-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
  -moz-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
  box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
}
#cssmenu > ul > li:hover > ul {
  opacity: 1;
  top: 65px;
  visibility: visible;
}
#cssmenu > ul > li > ul:before {
  content: '';
  display: block;
  border-color: transparent transparent #fafafa transparent;
  border-style: solid;
  border-width: 10px;
  position: absolute;
  top: -20px;
  left: 50%;
  margin-left: -10px;
}
#cssmenu > ul ul > li {
  position: relative;
}
#cssmenu ul ul a {
  color: #323232;
  font-family: Verdana, 'Lucida Grande';
  font-size: 13px;
  background-color: #fafafa;
  padding: 5px 8px 7px 16px;
  display: block;
  -webkit-transition: background-color 0.1s;
  -moz-transition: background-color 0.1s;
  -o-transition: background-color 0.1s;
  transition: background-color 0.1s;
}
#cssmenu ul ul a:hover {
  background-color: #f0f0f0;
}
#cssmenu ul ul ul {
  visibility: hidden;
  opacity: 0;
  position: absolute;
  top: -16px;
  left: 206px;
  padding: 16px 0 20px 0;
  background-color: #fafafa;
  text-align: left;
  width: 180px;
  -webkit-transition: all .3s;
  -moz-transition: all .3s;
  -o-transition: all .3s;
  transition: all .3s;
  -webkit-border-radius: 5px;
  -moz-border-radius: 5px;
  border-radius: 5px;
  -webkit-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
  -moz-box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
  box-shadow: 0px 1px 3px rgba(0, 0, 0, 0.4);
}
#cssmenu ul ul > li:hover > ul {
  opacity: 1;
  left: 190px;
  visibility: visible;
}
#cssmenu ul ul a:hover {
  background-color: #cc2c24;
  color: #f0f0f0;
}

最后是我的HTML。

<div id='cssmenu'>
<ul>
   <li class='active'><a href='index.html'><span>Home</span></a></li>
   <li><a href='#'><span>Forums</span></a></li>
   <li><a href='#'><span>Title1</span></a></li>
   <li><a href='#'><span>Title2</span></a></li>
   <li><a href='#'><span>Title3</span></a></li>
   <li class='last'><a href='#'><span>Title4</span></a></li>
</ul>
</div>

当前所有发生的事情是我的导航栏是100％的宽度，这是我想要的，但是按钮仍然向左对齐，我希望它们位于中间。我已经尝试了很多事情，但似乎无法使其正常工作。任何帮助是极大的赞赏。