我试图在 CSS 中将菜单项居中。该栏占据了屏幕的整个宽度，这是一个理想的结果。我希望菜单项相对于屏幕居中。
这是我使用的 CSS：
#cssmenu ul,
#cssmenu li,
#cssmenu span,
#cssmenu a {
margin: 0;
padding: 0;
position: relative;
}
#cssmenu {
height: 49px;
border-radius: 5px 5px 0 0;
-moz-border-radius: 5px 5px 0 0;
-webkit-border-radius: 5px 5px 0 0;
background: #141414;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%;
background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a), color-stop(100%, #141414));
background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
border-bottom: 2px solid #0fa1e0;
}
#cssmenu:after,
#cssmenu ul:after {
content: '';
display: block;
clear: both;
}
#cssmenu a {
background: #141414;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALElEQVQImWMwMrJi+v//PxMDw3+m//8ZoPR/qBgDEhuXGLoeYswhXg8R5gAAdVpfoJ3dB5oAAAAASUVORK5CYII=) 100% 100%;
background: -moz-linear-gradient(top, #32323a 0%, #141414 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #32323a), color-stop(100%, #141414));
background: -webkit-linear-gradient(top, #32323a 0%, #141414 100%);
background: -o-linear-gradient(top, #32323a 0%, #141414 100%);
background: -ms-linear-gradient(top, #32323a 0%, #141414 100%);
background: linear-gradient(to bottom, #32323a 0%, #141414 100%);
color: #ffffff;
display: inline-block;
font-family: Helvetica, Arial, Verdana, sans-serif;
font-size: 12px;
line-height: 49px;
padding: 0 20px;
text-decoration: none;
}
#cssmenu ul {
list-style: none;
}
#cssmenu > ul {
float: left;
}
#cssmenu > ul > li {
float: left;
}
#cssmenu > ul > li:hover:after {
content: '';
display: block;
width: 0;
height: 0;
position: absolute;
left: 50%;
bottom: 0;
border-left: 10px solid transparent;
border-right: 10px solid transparent;
border-bottom: 10px solid #0fa1e0;
margin-left: -10px;
}
#cssmenu > ul > li:first-child > a {
border-radius: 5px 0 0 0;
-moz-border-radius: 5px 0 0 0;
-webkit-border-radius: 5px 0 0 0;
}
#cssmenu > ul > li:last-child > a {
border-radius: 0 5px 0 0;
-moz-border-radius: 0 5px 0 0;
-webkit-border-radius: 0 5px 0 0;
}
#cssmenu > ul > li.active > a {
box-shadow: inset 0 0 3px #000000;
-moz-box-shadow: inset 0 0 3px #000000;
-webkit-box-shadow: inset 0 0 3px #000000;
background: #070707;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%;
background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c), color-stop(100%, #070707));
background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
}
#cssmenu > ul > li:hover > a {
background: #070707;
background:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAAxCAIAAACUDVRzAAAAA3NCSVQICAjb4U/gAAAALklEQVQImWNQU9Nh+v//PxMDw3+m//8ZkNj/mRgYIHxy5f//Z0BSi18e2TwS5QG4MGB54HL+mAAAAABJRU5ErkJggg==) 100% 100%;
background: -moz-linear-gradient(top, #26262c 0%, #070707 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #26262c), color-stop(100%, #070707));
background: -webkit-linear-gradient(top, #26262c 0%, #070707 100%);
background: -o-linear-gradient(top, #26262c 0%, #070707 100%);
background: -ms-linear-gradient(top, #26262c 0%, #070707 100%);
background: linear-gradient(to bottom, #26262c 0%, #070707 100%);
box-shadow: inset 0 0 3px #000000;
-moz-box-shadow: inset 0 0 3px #000000;
-webkit-box-shadow: inset 0 0 3px #000000;
}
#cssmenu .has-sub {
z-index: 1;
}
#cssmenu .has-sub:hover > ul {
display: block;
}
#cssmenu .has-sub ul {
display: none;
position: absolute;
width: 200px;
top: 100%;
left: 0;
}
#cssmenu .has-sub ul li {
*margin-bottom: -1px;
}
#cssmenu .has-sub ul li a {
background: #0fa1e0;
border-bottom: 1px dotted #6fc7ec;
filter: none;
font-size: 11px;
display: block;
line-height: 120%;
padding: 10px;
}
#cssmenu .has-sub ul li:hover a {
background: #0c7fb0;
}
#cssmenu .has-sub .has-sub:hover > ul {
display: block;
}
#cssmenu .has-sub .has-sub ul {
display: none;
position: absolute;
left: 100%;
top: 0;
}
#cssmenu .has-sub .has-sub ul li a {
background: #0c7fb0;
border-bottom: 1px dotted #6db2d0;
}
#cssmenu .has-sub .has-sub ul li a:hover {
background: #095c80;
}
此外，这是我使用的 HTML 代码：
<!DOCTYPE html>
<html lang="en">
<head>
<link href="menu_assets/styles.css" rel="stylesheet" type="text/css">
<link href="<?php echo base_url(); ?>menu_assets/styles.css" rel="stylesheet" type="text/css" />
<div id='cssmenu'>
<ul>
<li class='active'><a href='sample/home'><span>Home</span></a></li>
<li class='has-sub'><a href='#'><span>Upload Data</span></a>
<ul>
<li class='has-sub'><a href='sample/index'><span>Test Data</span></a>
<ul>
<li><a href='upload_form_att/index'><span>With Attachments</span></a></li>
<li class='last'><a href='sample/index'><span>Without Attachments</span></a></li>
</ul>
</li>
<li class='has-sub'><a href='#'><span>Protocol</span></a>
<ul>
<li><a href='#'><span>With Attachments</span></a></li>
<li class='last'><a href='#'><span>Without Attachments</span></a></li>
</ul>
</li>
</ul>
</li>
<li><a href='#'><span>Stability Data table</span></a></li>
<li><a href='#'><span>About</span></a></li>
<li class='last'><a href='#'><span>Logout</span></a></li>
</ul>
</div>
</head>
任何帮助，将不胜感激。
编辑：做出建议的更改后，我现在遇到了另一个问题。当我将鼠标悬停在“子菜单”项上时，“子子菜单”项会显示一个间隙，从而使它们无法点击。还有什么我需要编辑来解决这个问题吗？