I would like to make a position: fixed; popup box centered to the screen with a dynamic width and height. I used margin: 5% auto; for this. Without position: fixed; it centers fine horizontally, but not vertically. After adding position: fixed;, it's even not centering horizontally.
Here's the complete set:
.jqbox_innerhtml {
position: fixed;
width: 500px;
height: 200px;
margin: 5% auto;
padding: 10px;
border: 5px solid #ccc;
background-color: #fff;
}<div class="jqbox_innerhtml">
This should be inside a horizontally
and vertically centered box.
</div>How do I center this box in screen with CSS?
You basically need to set top and left to 50% to center the left-top corner of the div. You also need to set the margin-top and margin-left to the negative half of the div's height and width to shift the center towards the middle of the div.
Thus, provided a <!DOCTYPE html> (standards mode), this should do:
position: fixed;
width: 500px;
height: 200px;
top: 50%;
left: 50%;
margin-top: -100px; /* Negative half of height. */
margin-left: -250px; /* Negative half of width. */
Or, if you don't care about centering vertically and old browsers such as IE6/7, then you can instead also add left: 0 and right: 0 to the element having a margin-left and margin-right of auto, so that the fixed positioned element having a fixed width knows where its left and right offsets start. In your case thus:
position: fixed;
width: 500px;
height: 200px;
margin: 5% auto; /* Will not center vertically and won't work in IE6/7. */
left: 0;
right: 0;
Again, this works only in IE8+ if you care about IE, and this centers only horizontally not vertically.
I want to make a popup box centered to the screen with dynamic width and height.
Here is a modern approach for horizontally centering an element with a dynamic width - it works in all modern browsers; support can be seen here.
.jqbox_innerhtml {
position: fixed;
left: 50%;
transform: translateX(-50%);
}
For both vertical and horizontal centering you could use the following:
.jqbox_innerhtml {
position: fixed;
left: 50%;
top: 50%;
transform: translate(-50%, -50%);
}
You may wish to add in more vendor prefixed properties too (see the examples).
Or just add left: 0 and right: 0 to your original CSS, which makes it behave similarly to a regular non-fixed element and the usual auto-margin technique works:
.jqbox_innerhtml
{
position: fixed;
width:500px;
height:200px;
background-color:#FFF;
padding:10px;
border:5px solid #CCC;
z-index:200;
margin: 5% auto;
left: 0;
right: 0;
}
Note you need to use a valid (X)HTML DOCTYPE for it to behave correctly in IE (which you should of course have anyway..!)
Add a container like:
div {
position: fixed;
bottom: 0;
left: 0;
width: 100%;
text-align: center;
}
Then put your box into this div will do the work.
Just add:
left: calc(-50vw + 50%);
right: calc(-50vw + 50%);
margin-left: auto;
margin-right: auto;
This solution does not require of you to define a width and height to your popup div.
And instead of calculating the size of the popup, and minus half to the top, javascript is resizeing the popupContainer to fill out the whole screen...
(100% height, does not work when useing display:table-cell; (wich is required to center something vertically))...
Anyway it works :)
left: 0;
right: 0;
Was not working under IE7.
Changed to
left:auto;
right:auto;
Started working but in the rest browsers it stop working! So used this way for IE7 below
if ($.browser.msie && parseInt($.browser.version, 10) <= 7) {
strAlertWrapper.css({position:'fixed', bottom:'0', height:'auto', left:'auto', right:'auto'});
}
You can basically wrap it into another div and set its position to fixed.
.bg {
position: fixed;
width: 100%;
}
.jqbox_innerhtml {
width: 500px;
height: 200px;
margin: 5% auto;
padding: 10px;
border: 5px solid #ccc;
background-color: #fff;
}<div class="bg">
<div class="jqbox_innerhtml">
This should be inside a horizontally and vertically centered box.
</div>
</div>To fix the position use this :-
div {
position: fixed;
left: 68%;
transform: translateX(-8%);
}
I used vw (viewport width) and vh (viewport height). viewport is your entire screen. 100vw is your screens total width and 100vh is total height.
.class_name{
width: 50vw;
height: 50vh;
border: 1px solid red;
position: fixed;
left: 25vw;top: 25vh;
}
One possible answer:
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8">
<title>CSS Center Background Demo</title>
<style type="text/css">
body {
margin: 0;
padding: 0;
}
div.centred_background_stage_1 {
position: fixed;
z-index:(-1 );
top: 45%;
left: 50%;
}
div.centred_background_stage_2 {
position: relative;
left: -50%;
top: -208px;
/* % does not work.
According to the
http://reeddesign.co.uk/test/points-pixels.html
6pt is about 8px
In the case of this demo the background
text consists of three lines with
font size 80pt.
3 lines (with space between the lines)
times 80pt is about
~3*(1.3)*80pt*(8px/6pt)~ 416px
50% from the 416px = 208px
*/
text-align: left;
vertical-align: top;
}
#bells_and_wistles_for_the_demo {
font-family: monospace;
font-size: 80pt;
font-weight: bold;
color: #E0E0E0;
}
div.centred_background_foreground {
z-index: 1;
position: relative;
}
</style>
</head>
<body>
<div class="centred_background_stage_1">
<div class="centred_background_stage_2">
<div id="bells_and_wistles_for_the_demo">
World<br/>
Wide<br/>
Web
</div>
</div>
</div>
<div class="centred_background_foreground">
This is a demo for <br/>
<a href="http://stackoverflow.com/questions/2005954/center-element-with-positionfixed">
http://stackoverflow.com/questions/2005954/center-element-with-positionfixed
</a>
<br/><br/>
<a href="http://www.starwreck.com/" style="border: 0px;">
<img src="./star_wreck_in_the_perkinnintg.jpg"
style="opacity:0.1;"/>
</a>
<br/>
</div>
</body>
</html>
Try using this for horizontal elements that won't center correctly.
width: calc (width: 100% - width whatever else is off centering it)
For example if your side navigation bar is 200px:
width: calc(100% - 200px);
#modal {
display: flex;
justify-content: space-around;
align-items: center;
position: fixed;
left: 0;
top: 0;
width: 100%;
height: 100%;
}
inside it can be any element with diffenet width, height or without. all are centered.
The only foolproof solution is to use table align=center as in:
<table align=center><tr><td>
<div>
...
</div>
</td></tr></table>
I cannot believe people all over the world wasting these copious amount to silly time to solve such a fundamental problem as centering a div. css solution does not work for all browsers, jquery solution is a software computational solution and is not an option for other reasons.
I have wasted too much time repeatedly to avoid using table, but experience tell me to stop fighting it. Use table for centering div. Works all the time in all browsers! Never worry any more.
来源：https://stackoverflow.com/questions/2005954/center-a-positionfixed-element