问题

Is there a way to disable margin-collapsing altogether? The only solutions I\'ve found (by the name of \"uncollapsing\") entail using a 1px border or 1px padding. I find this unacceptable: the extraneous pixel complicates calculations for no good reason. Is there a more reasonable way to disable this margin-collapsing?

回答1:

There are two main types of margin collapse:

Collapsing margins between adjacent elements
Collapsing margins between parent and child elements

Using a padding or border will prevent collapse only in the latter case. Also, any value of overflow different from its default (visible) applied to the parent will prevent collapse. Thus, both overflow: auto and overflow: hidden will have the same effect. Perhaps the only difference when using hidden is the unintended consequence of hiding content if the parent has a fixed height.

Other properties that, once applied to the parent, can help fix this behaviour are:

float: left / right
position: absolute
display: inline-block

You can test all of them here: http://jsfiddle.net/XB9wX/1/.

I should add that, as usual, Internet Explorer is the exception. More specifically, in IE 7 margins do not collapse when some kind of layout is specified for the parent element, such as width.

Sources: Sitepoint's article Collapsing Margins

回答2:

You can also use the good old micro clearfix for this.

#container:before, #container:after{
    content: ' ';
    display: table;
}

See updated fiddle: http://jsfiddle.net/XB9wX/97/

回答3:

One neat trick to disable margin collapsing that has no visual impact, as far as I know, is setting the padding of the parent to 0.05px:

.parentClass {
    padding: 0.05px;
}

The padding is no longer 0 so collapsing won't occur anymore but at the same time the padding is small enough that visually it will round down to 0.

If some other padding is desired, then apply padding only to the "direction" in which margin collapsing is not desired, for example padding-top: 0.05px;.

Working example:

.noCollapse {
  padding: 0.05px;
}

.parent {
  background-color: red;
  width: 150px;
}

.children {
  margin-top: 50px;

  background-color: lime;      
  width: 100px;
  height: 100px;
}

<h3>Border collapsing</h3>
<div class="parent">
  <div class="children">
  </div>
</div>

<h3>No border collapsing</h3>
<div class="parent noCollapse">
  <div class="children">
  </div>
</div>

Edit: changed the value from 0.1 to 0.05. As Chris Morgan mentioned in a comment bellow, and from this small test, it seems that indeed Firefox takes the 0.1px padding into consideration. Though, 0.05px seemes to do the trick.

回答4:

overflow:hidden prevents collapsing margins but it's not free of side effects - namely it... hides overflow.

Apart form this and what you've mentioned you just have to learn live with it and learn for this day when they are actually useful (comes every 3 to 5 years).

回答5:

Actually, there is one that works flawlessly:

display: flex; flex-direction: column;

as long as you can live with supporting only IE10 and up

.container {
  display: flex;
  flex-direction: column;
    background: #ddd;
    width: 15em;
}

.square {
    margin: 15px;
    height: 3em;
    background: yellow;
}

<div class="container">
    <div class="square"></div>
    <div class="square"></div>
    <div class="square"></div>
</div>
<div class="container">
    <div class="square"></div>
    <div class="square"></div>
    <div class="square"></div>
</div>

回答6:

Every webkit based browser should support the properties -webkit-margin-collapse. There are also subproperties to only set it for the top or bottom margin. You can give it the values collapse (default), discard (sets margin to 0 if there is a neighboring margin), and separate (prevents margin collapse).

I've tested that this works on 2014 versions of Chrome and Safari. Unfortunately, I don't think this would be supported in IE because it's not based on webkit.

Read Apple's Safari CSS Reference for a full explanation.

If you check Mozilla's CSS webkit extensions page, they list these properties as proprietary and recommend not to use them. This is because they're likely not going to go into standard CSS anytime soon and only webkit based browsers will support them.

回答7:

I know that this is a very old post but just wanted to say that using flexbox on a parent element would disable margin collapsing for its child elements.

回答8:

I had similar problem with margin collapse because of parent having position set to relative. Here are list of commands you can use to disable margin collapsing.

HERE IS PLAYGROUND TO TEST

Just try to assign any parent-fix* class to div.container element, or any class children-fix* to div.margin. Pick the one that fits your needs best.

When

margin collapsing is disabled, div.absolute with red background will be positioned at the very top of the page.
margin is collapsing div.absolute will be positioned at the same Y coordinate as div.margin

html, body { margin: 0; padding: 0; }

.container {
  width: 100%;
  position: relative;
}

.absolute {
  position: absolute;
  top: 0;
  left: 50px;
  right: 50px;
  height: 100px;
  border: 5px solid #F00;
  background-color: rgba(255, 0, 0, 0.5);
}

.margin {
  width: 100%;
  height: 20px;
  background-color: #444;
  margin-top: 50px;
  color: #FFF;
}

/* Here are some examples on how to disable margin 
   collapsing from within parent (.container) */
.parent-fix1 { padding-top: 1px; }
.parent-fix2 { border: 1px solid rgba(0,0,0, 0);}
.parent-fix3 { overflow: auto;}
.parent-fix4 { float: left;}
.parent-fix5 { display: inline-block; }
.parent-fix6 { position: absolute; }
.parent-fix7 { display: flex; }
.parent-fix8 { -webkit-margin-collapse: separate; }
.parent-fix9:before {  content: ' '; display: table; }

/* Here are some examples on how to disable margin 
   collapsing from within children (.margin) */
.children-fix1 { float: left; }
.children-fix2 { display: inline-block; }

<div class="container parent-fix1">
  <div class="margin children-fix">margin</div>
  <div class="absolute"></div>
</div>

Here is jsFiddle with example you can edit

回答9:

For your information you could use grid but with side effects :)

.parent {
  display: grid
}

来源：https://stackoverflow.com/questions/19718634/how-to-disable-margin-collapsing

标签

css

css3

margin

collapse

How to disable margin-collapsing?

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