I have the following DIV inside a body tag:
Yes
And these are their CSS classes
You can add line-height:51px to #AlertDiv h1 if you know it's only ever going to be one line. Also add text-align:center to #AlertDiv.
#AlertDiv {
top:198px;
left:365px;
width:62px;
height:51px;
color:white;
position:absolute;
text-align:center;
background-color:black;
}
#AlertDiv h1 {
margin:auto;
line-height:51px;
vertical-align:middle;
}
The demo below also uses negative margins to keep the #AlertDiv centered on both axis, even when the window is resized.
Demo: jsfiddle.net/KaXY5