Summary of issues related to horizontal and vertical centering of html_HTML/Xhtml_Web page production

I have encountered a lot of centering problems recently, so I took some time to summarize them here so that they can be easily found in the future

1. Centered text

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Code As follows:

I am in the middle...

.. height line-height text-center（ Can only center a single line)
.wrap{
width:px;
height:px;
border:px solid red;
text-align: center;
line-height: px;
}

ps:text-align:center just centers the inline elements below the element
1.2display:table-cell (Multiple lines with fixed height centered)

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The code is as follows:

.wrap{
width:px;
height:px;
border:px solid red;
text-align: center;
display:table-cell;
vertical- align: middle;
}

display:table-cell: It doesn’t work in ie67, it’s best to use it together with display:table;
ie67: (It won’t be used in the future. , but let’s put it here)
Method 1: (The height of the em tag is equal to the height of the parent, so centering span and em is equivalent to centering span on the parent)

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The code is as follows:

I am in the middle... I am in the middle... I am in the middle... I am in the middle...

.wrap{
width:px;
height:px;
border:px solid red;
text-align: center;
}
.wrap span{
vertical-align: middle;
display:inline-block;
width:px;
}
.wrap em{
height:%;
vertical-align: middle;
display:inline-block;
}

Method 2: (By adding an absolutely positioned parent tag to the child element, and then matching the relative positioning of the child element to center it horizontally and vertically)

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The code is as follows:

I am in the middle... I am in the middle... I am in the middle... I am in the middle...

.wrap{
width:px;
height:px;
border:px solid red;
display:table;
position:relative;
overflow: hidden;
}
.wrap .span{
display:table-cell;
vertical-align: middle;
text-align: center;
*position: absolute;
top:%;
left:%;
}
.wrap .span{
*position:relative;
top:-%;
left:- %;
}

1.3padding (inner padding, needless to say)

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The code is as follows :

.wrap{
width:px;
border:px solid red;
padding:px ;
}

2. Centered element

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The code is as follows :

2.1position:absolute negative margin (width and height must be available to calculate margin)

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The code is as follows:

.wrap{
width:px;
height:px;
position:absolute;
top:%;
left:%;
margin-top :-px;
margin-left:-px;
border:px solid red;
}
.wrap span{
width:px;
height:px;
> background:red;
position: absolute;
top:%;
left:%;
margin-top:-px;
margin-left:-px;
}

ps: CSS implements horizontal centering and vertical centering of DIVs

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code As follows:

DIV is centered horizontally and vertically up and downDIVCSS5

< ;/html>

Introduction to the principle of horizontal and vertical centering
Absolute positioning position:absolute is used here. Use left and top to set the object distance to the top and left to 50%, but if it is set to 50%, the box is actually The centering effect is not achieved, so margin-left:-200px;margin-top:-100px; is set. The trick here is that the value of margin-left is half the width, and the value of margin-top is also half the height of the object. At the same time, set is negative, thus achieving horizontal and vertical centering.