CSS margin terror; Margin adds space outside paren

2018-12-31 01:14发布

站内问答 / HTML/CSS
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My css margins doesn't behave the way I want or expect them to. I seems like my header margin-top affect the div-tags surrounding it.

This is what I want and expect: What I want....

...but this is what I end up with: What I get...

Source:

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>Margin test</title>

<style type="text/css">
body {
    margin:0;
}
#page {
    margin:0;
    background:#FF9;
}
#page_container {
    margin:0 20px;
}
h1 {
    margin:50px 0 0 0;
}
</style>

</head>

<body>

<div id="page">
    <div id="page_container">
        <header id="branding" role="banner">
            <hgroup>
                <h1 id="site-title"><span><a href="#" title="Title" rel="home">Title</a></span></h1>
                <h2 id="site-description">Description</h2>
            </hgroup>
        </header>
    </div>
</div>

I have exaggerated the margin in this example. Default browser margin on h1-tag is somewhat smaller, and in my case I use Twitter Bootstrap, with Normalizer.css which sets default margin to 10px. Not that important, main point is; I can not, should not, want not change the margin on the h1-tag.

I guess it is similar to my other question; Why does this CSS margin-top style not work?. Question is how do I solve this specific issue?

I have read a few threads on similar problems, but haven't found any real answers and solutions. I know adding padding:1px; or border:1px; solves the problem. But that only adds new problems, since I do not want a padding nor a border on my div-tags.

There must be a better, best practice, solution? This must be pretty common.

5条回答
只若初见
2楼-- · 2018-12-31 01:27

The solutions in the other answers didn't work for me. Transparent borders, inline-block, etc., all caused other problems. Instead, I added the following css to my ancestor element:

parent::after{
  content: "";
  display: inline-block;
  clear: both;
}

Depending on your situation, this may cause its own problems because it adds extra space after the last child element.

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妖精总统
3楼-- · 2018-12-31 01:34

Add any one of the following rules:

float: left/right;
position: absolute;
display: inline-block;
overflow: auto/scroll/hidden;
clear: left/right/both;

This is caused by collapsing margins. See an article about this behavior here.

According to the article:

The W3C specification defines collapsing margins as follows:

“In this specification, the expression collapsing margins means that adjoining margins (no non-empty content, padding, or border areas, or clearance separate them) of two or more boxes (which may be next to one another or nested) combine to form a single margin.”

This is also true for parent-child elements.

All the answers include one of the possible solutions:

There are other situations where elements do not have their margins collapsed:

  • floated elements
  • absolutely positioned elements
  • inline-block elements
  • elements with overflow set to anything other than visible (They do not collapse margins with their children.)
  • cleared elements (They do not collapse their top margins with their parent block’s bottom margin.)
  • the root element
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怪性笑人.
4楼-- · 2018-12-31 01:35

Problem was the parent not taking into account children for height. Adding display:inline-block; did it for me.

Full CSS

#page {
    margin:0;
    background:#FF9;
    display:inline-block;
    width:100%;
}

See Fiddle

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牵手、夕阳
5楼-- · 2018-12-31 01:49

Just add border-top: 1px solid transparent; to your #page element.

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何处买醉
6楼-- · 2018-12-31 01:50

Add overflow:auto to your #page div.

jsFiddle example

And check out collapsing margins while you're at it.

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