Vertical align center of absolute div - css

Question

I have this simple HTML code, but make me frustrated because it can't center vertically :
<div class="outer">
<div class="inner">
Hello World
</div>
</div>
and here's my CSS :
.outer {
position: relative;
height: 350px;
}
.inner {
position: absolute;
height: 100px;
top: 50%
}
the .inner div is really center vertically, but based on top side of it. because of top: 50%, what I want is this .inner div really centered vertically on top of .outer. how to do that?

Answer 1

You can center your element using css3 even if you don't know the dimensions.
.inner {
position: absolute;
height: 100px;
top: 50%;
transform: translateY(-50%);
-webkit-transform: translateY(-50%);
}

Answer 2

Since you know the height of both elements you can set your top to top: 125px;
(350 - 100) / 2.
UPDATED WITH JQUERY
http://jsfiddle.net/yf0ncd7f/

Answer 3

Actually an easy way to center a absolute div is to use margin: auto;
section {
width: 100%;
height: 800px;
position: relative;
background: #eee;
}
div {
width: 500px;
height: 300px;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
margin: auto;
background: orange;
}
<section>
<div></div>
</section>

Answer 4

I added borders to differentiate clearly
Is this you want?
http://plnkr.co/edit/JRct1x95gnIUl8jITzG0?p=preview
.outer {
position: relative;
height: 150px;
border : 1px solid #f00;
}
.inner {
position: absolute;
height: 80px;
top:0;
bottom:0;
margin:auto;
border : 1px solid #0f0;
}

Answer 5

You could use this CSS trick to make the div vertically centered (and optionally horizontally as well). This works for a parent div of any height and width, as long as they are specified.
.inner {
position:absolute;
// The height and width of the element have to be set for this to work
height:100px;
width:100px;
// Setting the top and bottom to 0px as well as the margins to auto
// causes the div to be centered vertically.
top: 0px;
bottom: 0px;
margin-top: auto;
margin-bottom: auto;
// To also center the div horizontally, do the same for
// left, right and the margins.
left: 0px;
right: 0px;
margin-left:auto;
margin-right:auto;
}
Note that this solution only works when the height of the parent div is known beforehand and is specified. So the parent element needs to have height:100px or whatever amount of pixels you need it to be. Also the height can't be percentual, meaning that if the height of the parent div is declared as height:50%, this will NOT work.
The inner div can actually have a

Answer 6

You can set it by line-height property set it to the height of the div as in your code it should be line-height: 100px;
.outer {
position: relative;
height: 350px;
background: gray;
}
.inner {
position: absolute;
height: 100px;
line-height: 100px;
background: blue;
}
<div class="outer">
<div class="inner">
Hello World
</div>
</div>