Html 为什么我不能以 margin: 0 auto 居中？
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Why can't I center with margin: 0 auto?
提问by zeckdude
I have a #headerdiv that is 100% widthand within that div I have an unordered list. I have applied margin: 0 autoto the unordered list but it won't center it within the header div.
我有一个#headerdiv，100% width在那个 div 中我有一个无序列表。我已经申请margin: 0 auto了无序列表，但它不会在标题 div 中居中。
Can anybody please tell me why? I thought that if I define the width of the parent div, then the unordered list should be able to center itself with margin: 0 auto. What am I missing?
谁能告诉我为什么？我认为如果我定义父 div 的宽度，那么无序列表应该能够以margin: 0 auto. 我错过了什么？
Here is my code:
这是我的代码：
<style>
* {
margin: 0;
padding: 0;
}
#header {
width: 100%;
background-color: #333;
min-height: 160px;
font-family:Arial, Helvetica, sans-serif;
}
#sitename {
font-size: 50px;
width: 620px;
margin:0 auto;
padding-top: 35px;
color:#999;
}
#header ul {
float: right;
margin: 0 auto;
}
#header ul li {
float: left;
padding-right: 20px;
list-style-type: none;
font-size: 20px;
}
</style>
</head>
<body>
<div id="header">
<h1 id="sitename">Photography Auction Site</h1>
<ul>
<li>List of Photos</li>
<li>Image Gallery</li>
<li>Contact Us</li>
</ul>
</div>
</body>
</html>
回答by PatrikAkerstrand
You need to define the width of the element you are centering, not the parent element.
您需要定义要居中的元素的宽度，而不是父元素的宽度。
#header ul {
margin: 0 auto;
width: 90%;
}
Edit: Ok, I've seen the testpage now, and here is how I think you want it:
编辑：好的，我现在已经看到了测试页，这是我认为你想要的：
#header ul {
list-style:none;
margin:0 auto;
width:90%;
}
/* Remove the float: left; property, it interferes with display: inline and
* causes problems. (float: left; makes the element implicitly a block-level
* element. It is still good to use display: inline on it to overcome a bug
* in IE6 and below that doubles horizontal margins for floated elements)
* The styles below is the full style for the list-items.
*/
#header ul li {
color:#CCCCCC;
display:inline;
font-size:20px;
padding-right:20px;
}
回答by Hoeks
An inline-block covers the whole line (from left to right), so a margin left and/or right won't work here. What you need is a block, a block has borders on the left and the right so can be influenced by margins.
内联块覆盖整行（从左到右），因此左边距和/或右边距在这里不起作用。你需要的是一个块，一个块的左右都有边界，所以可能会受到边距的影响。
This is how it works for me:
这对我来说是这样的：
#content {
display: block;
margin: 0 auto;
}
回答by kalys.osmonov
Why not?
为什么不？
#header {
text-align: center;
}
#header ul {
display: inline;
}
回答by bill dou
I don't know why the first answer is the best one, I tried it and not working in fact, as @kalys.osmonov said, you can give text-align:centerto header, but you have to make ulas inline-blockrather than inline, and also you have to notice that text-aligncan be inherited which is not good to some degree, so the better way (not working below IE 9) is using marginand transform. Just remove float rightand margin;0 autofrom ul, like below:
我不知道为什么第一个答案是最好的，我尝试过了，其实不是工作，如@ kalys.osmonov说，你可以给text-align:center到header，但你必须做ul的inline-block，而不是inline和你也必须通知其text-align可以继承，这是不好的一定程度，以便更好的方式（不工作下面IE 9）正在使用margin和transform。只需删除float right和margin;0 autofrom ul，如下所示：
#header ul {
/* float: right; */
/* margin: 0 auto; */
display: inline-block;
margin-left: 50%; /* From parent width */
transform: translateX(-50%); /* use self width which can be unknown */
-ms-transform: translateX(-50%); /* For IE9 */
}
This way can fix the problem that making dynamic width of ulcenter if you don't care IE8 etc.
ul如果你不关心IE8等，这种方式可以解决动态中心宽度的问题。
回答by Vani S
We can set the width for ul tag then it will align center.
我们可以设置 ul 标签的宽度，然后它会居中对齐。
#header ul {
display: block;
margin: 0 auto;
width: 420px;
max-width: 100%;
}
