CSS ::before ::after 类的伪元素不起作用
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CSS ::before ::after pseudo-element of class not working
提问by dub stylee
I am trying to add a ::beforeand ::afterpseudo-element to a menu heading. The pseudo-elements work fine for a regular link outside of the menu. However, when I am trying to apply them to a menu item, the backgroundproperty is set, but the ::beforeand ::afterproperties are not.
我正在尝试向菜单标题添加一个::before和::after伪元素。伪元素适用于菜单外的常规链接。但是，当我尝试将它们应用于菜单项时，background属性已设置，但::before和::after属性未设置。
Here is the relevant CSS:
这是相关的CSS：
#cssmenu {
background-color: #FFFFCC;
clear: both;
display: inline;
float: left;
list-style: none;
overflow: hidden;
text-align: center;
text-transform: uppercase;
width: 100%;
}
#cssmenu li {
display: inline-block;
}
#cssmenu li a {
display: inline-block;
}
#cssmenu li ul {
/*margin-top: 0px; submenu location relative to bottom of parent */
display: none;
}
#cssmenu li:hover ul {
display: block;
position: absolute;
}
#cssmenu li ul li a {
width: 200px;
}
#cssmenu li:hover > a {
/* shadow around parent when hover */
box-shadow: 5px 5px 25px #000;
-moz-box-shadow: 5px 5px 25px #000;
-webkit-box-shadow: 5px 5px 25px #000;
}
#cssmenu li a {
color: #000;
font-weight: bold;
text-decoration: none;
padding: 0 12px;
line-height: 24px;
}
#cssmenu li a:hover {
background-color: #99CC99;
/*padding: 12px; link background when hover over link */
}
#cssmenu li ul {
background: rgba(255,255,255,0.9); child menu background w/ transparency
padding: 10px 5px;
box-shadow: 5px 5px 25px #BBB;
-moz-box-shadow: 5px 5px 25px #BBB;
-webkit-box-shadow: 5px 5px 25px #BBB;
border-radius: 0px 15px 15px 15px;
-moz-border-radius: 0px 15px 15px 15px;
-webkit-border-radius: 0px 5px 5px 5px;
}
/* display sub-menu as list */
#cssmenu li ul li {
display: block;
text-align: left;
}
#cssmenu li ul li a, #nav li ul li a:hover {
background: transparent;
color: #000;
width: 180px;
font-size: 0.95em;
font-weight: normal;
padding: 6px;
}
#cssmenu li ul li a:hover {
/*text-decoration: underline;*/
box-shadow: none;
-moz-box-shadow: none;
-webkit-box-shadow: none;
border-radius: 0;
-moz-border-radius: 0;
-webkit-border-radius: 0;
}
.menuheader {
/* allow for the pseudo-elements which do not have layout due to absolute positioning */
margin: 12px 15px;
border: 0;
background: url("../../../images/buttonslice24.png") 24px 0 repeat-x ;
}
.menuheader::before,
.menuheader::after {
content: ' ';
position: absolute;
top: 0;
width: 12px;
height: 24px;
}
.menuheader::before {
left: -12px;
background: url("../../../images/buttonleft24.png") 0 0;
no-repeat;
}
.menuheader::after {
right: -12px;
background: url("../../../images/buttonright24.png") 100% 0;
no-repeat;
}
And the relevant HTML:
以及相关的 HTML：
<div id="cssmenu">
<ul>
<li><a class="menuheader" href="../../../contact-us.aspx">Contact</a></li>
<li><a class="menuheader" href="../../../">Home</a></li>
<li><a class="menuheader">Store</a>
<ul>
<li><a href="../../../shipping-policy.aspx">Shipping & Return Policy</a></li>
</ul>
</li>
<li><a class="menuheader" href="../../../account.aspx">Account</a></li>
<li><a class="menuheader" href="../../../cart.aspx">View Cart</a></li>
</ul>
</div>
I have also tried to reference the menuheaderclass items by #cssmenu ul li ainstead, and that actually works (sort of). Instead of the ::beforeand ::afterimages showing next to the menu item itself, they show next to the first item in the drop-down menu.
我也尝试通过引用menuheader类项#cssmenu ul li a，这实际上有效（有点）。它们不是显示在菜单项本身旁边的::before和::after图像，而是显示在下拉菜单中的第一项旁边。
I have read other questions on here regarding pseudo-elements, as well as http://www.w3schools.com/css/css_pseudo_elements.aspand as far as I can tell, the ::beforeand ::aftershould be able to be applied to an <a>element. This may be some simple issue, but I am just not seeing the issue here.
我在这里阅读了有关伪元素的其他问题，以及http://www.w3schools.com/css/css_pseudo_elements.asp，据我所知，::before和::after应该能够应用于<a>元素。这可能是一些简单的问题，但我只是没有在这里看到这个问题。
回答by Jasper
If you're going to absolutely position the pseudo elements, you need to give their parent a positionvalue, same as with non-pseudo elements.
如果你要绝对定位伪元素，你需要给它们的父元素一个position值，与非伪元素相同。
Just add:
只需添加：
.menuheader {
position : relative;
}
Here is an updated version of your JSFiddle (the only changes are adding the above code and making the background of the pseudo elements a solid color for demonstration): http://jsfiddle.net/99Aq8/1/
这是您的 JSFiddle 的更新版本（唯一的变化是添加上面的代码并使伪元素的背景成为演示的纯色）：http: //jsfiddle.net/99Aq8/1/
