如何使能DIV垂直和水平居中

<style type="text/css">

.center-middle1 {

position:absolute;

background-color: #e2e2e2;

width: 100%;

height: 300px;

top:50%;

margin-top: -150px; }

.center-middle2 {

position:absolute;

background-color: #e2e2e2;

width: 300px;

height: 200px;

left:50%;

top:50%;

margin-left: -150px;

margin-top: -100px; }

</style>

用例:

<div class="enter-middle2">

如何使能DIV垂直和水平居中

</div>