使用 CSS 将元素放在前面

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最佳答案

Add z-index:-1 and position:relative to .content

#header {
background: url(http://placehold.it/420x160) center top no-repeat;
}
#header-inner {
background: url(http://placekitten.com/150/200) right top no-repeat;
}
.logo-class {
height: 128px;
}
.content {
margin-left: auto;
margin-right: auto;
table-layout: fixed;
border-collapse: collapse;
z-index: -1;
position:relative;
}
.td-main {
text-align: center;
padding: 80px 10px 80px 10px;
border: 1px solid #A02422;
background: #ABABAB;
}

<body>
<div id="header">
<div id="header-inner">
<table class="content">
<col width="400px" />
<tr>
<td>
<table class="content">
<col width="400px" />
<tr>
<td>
<div class="logo-class"></div>
</td>
</tr>
<tr>
<td id="menu"></td>
</tr>
</table>
<table class="content">
<col width="120px" />
<col width="160px" />
<col width="120px" />
<tr>
<td class="td-main">text</td>
<td class="td-main">text</td>
<td class="td-main">text</td>
</tr>
</table>
</td>
</tr>
</table>
</div>
<!-- header-inner -->
</div>
<!-- header -->
</body>

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Note: z-index only works on positioned elements (position:absolute, position:relative, or position:fixed). Use one of those.

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In my case i had to move the html code of the element i wanted at the front at the end of the html file, because if one element has z-index and the other doesn't have z index it doesn't work.

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Another Note: z-index must be considered when looking at children objects relative to other objects.

For example

<div class="container">
<div class="branch_1">
<div class="branch_1__child"></div>
</div>
<div class="branch_2">
<div class="branch_2__child"></div>
</div>
</div>

If you gave branch_1__child a z-index of 99 and you gave branch_2__child a z-index of 1, but you also gave your branch_2 a z-index of 10 and your branch_1 a z-index of 1, your branch_1__child still will not show up in front of your branch_2__child

Anyways, what I'm trying to say is; if a parent of an element you'd like to be placed in front has a lower z-index than its relative, that element will not be placed higher.

The z-index is relative to its containers. A z-index placed on a container farther up in the hierarchy basically starts a new "layer"

Incep[inception]tion

Here's a fiddle to play around:

https://jsfiddle.net/orkLx6o8/