Changing the margin-top of a nested div within a parent container div will cause both elements to be displaced downwards from the main body

Question

Changing the margin-top of a nested div within a parent container div will cause both elements to be displaced downwards from the main body

I am facing an issue that I believe is a result of something silly I may have done, but I can't seem to pinpoint it. Here's a demonstration page illustrating my problem. Below is the source code for the page:

<html>
<head>
    <title>demo</title>
    <style type='text/css'>
        body{
            margin: 0px;
            padding: 0px;
        }
        #container{
            height: 100%;
            background-color: black;
        }
        #logo{
            margin: 25px auto auto auto;
            width: 360px;
            height: 45px;
            background-color: goldenrod;
        }
    </style>
</head>
<body>
    <div id='container'>
        <div id='logo'>
            <p>logotext.</p>
        </div>
    </div>
</body>
</html>

The issue arises as the top value of margin is adjusted, causing both #logo and #container to shift down the page. Ideally, #container should remain fixed while #logo moves downward on the page.

css html margin

Answer 1

Answer №1

The issue at hand is due to collapsing margins. When two elements have touching margins, those margins merge together. For a detailed explanation of this concept, visit this link and refer to the section titled

Collapsing Margins Between Parent and Child Elements

.

There are three possible solutions:

One solution is to apply overflow: auto to the container. This will alter the Block Formatting Context (BCF). More information on this technique can be found here.

#container {
    height: 100%;
    background-color: black;
    /* Add oveflow auto to container */
    overflow: auto;
}

View the implementation here: http://jsfiddle.net/bzVgV/20/

Another approach is to use padding on the container instead of a margin on the logo. This eliminates margins from affecting the layout.

#container {
    height: 100%;
    background-color: black;
    /* Use padding on container instead of margin on logo */
    padding-top: 30px;
}

Check out the result here: http://jsfiddle.net/bzVgV/18/

A final option is to prevent the margins from touching by adding a 1px padding to the parent element.

#container {
    height: 100%;
    background-color: black;
    /* Now margins of container and logo won't touch */
    padding-top: 1px;
}

See the change in action here: http://jsfiddle.net/bzVgV/21/

Answer 2

The issue at hand is due to collapsing margins. When two elements have touching margins, those margins merge together. For a detailed explanation of this concept, visit this link and refer to the section titled

Collapsing Margins Between Parent and Child Elements

.

There are three possible solutions:

One solution is to apply overflow: auto to the container. This will alter the Block Formatting Context (BCF). More information on this technique can be found here.

#container {
    height: 100%;
    background-color: black;
    /* Add oveflow auto to container */
    overflow: auto;
}

View the implementation here: http://jsfiddle.net/bzVgV/20/

Another approach is to use padding on the container instead of a margin on the logo. This eliminates margins from affecting the layout.

#container {
    height: 100%;
    background-color: black;
    /* Use padding on container instead of margin on logo */
    padding-top: 30px;
}

Check out the result here: http://jsfiddle.net/bzVgV/18/

A final option is to prevent the margins from touching by adding a 1px padding to the parent element.

#container {
    height: 100%;
    background-color: black;
    /* Now margins of container and logo won't touch */
    padding-top: 1px;
}

See the change in action here: http://jsfiddle.net/bzVgV/21/

Changing the margin-top of a nested div within a parent container div will cause both elements to be displaced downwards from the main body

Answer №1

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