Horizontal Align

1. Text-Align: Center;
div{
    text-align: center;
}

2. Margin: 0 auto;

CAUTION : To use this you must fixe the tag/div ... Width
body{
    width : 500px;
    margin: 0 auto;
}

NOTE : You must be carefull about
display:block; display:inline; .....

More : 
Align : http://www.w3schools.com/css/css_align.asp
Width: Calc(): http://stackoverflow.com/questions/14814616/calculating-width-from-percent-to-pixel-then-minus-by-pixel-in-less-css

3. Example with transform:
position: absolute;
top: 25%;
left: 50%;
transform: translate(-50%, -50%);