Center A Position:fixed Element


Answer :

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.

Updated Example

.jqbox_innerhtml {     position: fixed;     left: 50%;     transform: translateX(-50%); }

For both vertical and horizontal centering you could use the following:

Updated Example

.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..!)


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