CSS: Margin-top when parent's got no border

问题

As you can see in this picture, I've got an orange div inside a green div with no top border. The orange div has a 30px top margin, but it's also pushing the green div down. Of course, adding a top border will fix the issue, but I need the green div to be top borderless. What could I do?

.body {
	border: 1px solid black;
	border-top: none;
	border-bottom: none;
	width: 120px;
	height: 112px;
	background-color: lightgreen;
}

.body .container {
	background-color: orange;
	height: 50px;
	width: 50%;
	margin-top: 30px;
}

<div class="header">Top</div>
<div class="body">
	<div class="container">Box</div>
</div>
<div class="foot">Bottom</div>

Thanks

回答1:

You could add overflow:auto to .body to prevent margin-collapsing. See http://www.w3.org/TR/CSS2/box.html#collapsing-margins

回答2:

What you experience is margin collapsing. The margin doesn't specify an area around an element, but rather the minimum distance between elements.

As the green container doesn't have any border or padding, there is nothing to contain the margin of the orange element. The margin is used between the top element and the orange element just as if the green container would have the margin.

Use a padding in the green container instead of a margin on the orange element.

回答3:

Use padding instead of margin:

.body .container {
    ...
    padding-top: 30px;
}

回答4:

Not sure if this will work in your case, but I just solved this with the following CSS properties

#element {
    padding-top: 1px;
    margin-top: -1px;
}

#element was being pushed down because it's first child element had a margin-top: 30px. With this CSS, it now works as expected :) Not sure if it'll work for every case, YMMV.

回答5:

You can either add padding-top: 30 on the green box, use relative positioning on the orange box with top: 30px, or float the orange box and use the same margin-top: 30px.

回答6:

You read this document: Box model - Margin collapsing

CSS

.body {
    border: 1px solid black;
    border-bottom: none;
    border-top: none;
    width: 120px;
    height: 112px;
    background-color: lightgreen;
    padding-top: 30px;
}

.body .container {
    background-color: orange;
    height: 50px;
    width: 50%;
}

回答7:

Not sure how hackish this sounds, but how about adding a transparent border?

来源：https://stackoverflow.com/questions/1394724/css-margin-top-when-parents-got-no-border

标签

css

border

margin

collapse