Want to center a div - css

Question

Hi my problem is that I actually can't center my div!
it's always stuck on the left. I already tried the margin-left: auto; and margin-right: auto;, but it doen't seems to work.
Here's the HTML:
<ul class="menu">
<li>Acceuil</li>
<li>LoL
<ul>
<li><a><span class="headlist">League of Legends</a></li>
<li>Funny games</li>
<li>Favorite builds</li>
<li>...</li>
</ul>
</li>
<li>SSF2
<ul>
<li><a><span class="headlist">Super Smash Flash 2</a>
<li>Intro</li>
<li>Events</li>
<li>Challenges</li>
</ul>
</li>
<li>RotMG</li>
<li>GMod</li>
<li>Contact</li>
</ul>
<div>
<p>
HUEHUEHUEHUEHUEHUEHUE
</p>
</div>
And here's the css:
html {
background: url(bg.jpg) no-repeat center center fixed;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
/* div */
div
{
text-align: center;
border-radius: 0 0 5px 5px;
width: 590px;
padding-left: 5px;
padding-right: 5px;
padding-top: 5px;
padding-bottom: 5px;
background-color: rgba(140,0,0,0.7);
margin-left: auto;
margin-right: auto;
text-shadow: 1px 1px 1px rgba(0,0,0,.5);
color: #f3f3f3;
font-family: Helvetica, Arial, sans-serif;
display: block;
position: absolute;
top: 38px;
left: 25%;
z-index: -50;
margin-left: auto;
margin-right: auto;
}
/* Reset de la liste (aucun style, etc.) */
.menu,
.menu ul,
.menu li,
.menu a,
.menu p
{
margin: 0;
padding: 0;
border: none;
outline: none;
}
/* Menu */
.menu
{
height: 40px;
width: 610px; /* Longueur du menu */
background: #760101; /* couleur du gradient */
background: -moz-linear-gradient(#D20202, #760101);
background: -webkit-gradient(linear,left bottom,left top,color-stop(0, #760101),color-stop(1, #D20202));
background: -webkit-linear-gradient(#D20202, #760101);
background: -o-linear-gradient(#D20202, #760101);
background: -ms-linear-gradient(#D20202, #760101);
background: linear-gradient(#D20202, #760101);
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 13px;
display: block;
margin-left: auto;
margin-right: auto;
}
.menu li {
position: relative;
list-style: none;
float: left;
display: block;
height: 40px;
}
.menu li a {
display: block;
padding: 0 7px 0 40px;
margin: 6px 0;
line-height: 28px;
text-decoration: none;
border-left: 1px solid #4B0101;
border-right: 1px solid #5C0101;
font-family: Helvetica, Arial, sans-serif;
font-weight: bold;
font-size: 13px;
color: #f3f3f3;
text-shadow: 1px 1px 1px rgba(0,0,0,.6);
-webkit-transition: color .2s ease-in-out;
-moz-transition: color .2s ease-in-out;
-o-transition: color .2s ease-in-out;
-ms-transition: color .2s ease-in-out;
transition: color .2s ease-in-out;
}
.menu li:first-child a { border-left: none; }
.menu li:last-child a{ border-right: none; }
.menu li:hover > a { color: #FF9900; }
/* Sub-menu */
.menu ul {
position: absolute;
top: 40px;
left: 0;
opacity: 0;
background: #D20202;
background: -moz-linear-gradient(#760101, #D20202);
background: -webkit-gradient(linear,left bottom,left top,color-stop(0, #D20202),color-stop(1, #760101));
background: -webkit-linear-gradient(#760101, #D20202);
background: -o-linear-gradient(#760101, #D20202);
background: -ms-linear-gradient(#760101, #D20202);
background: linear-gradient(#760101, #D20202);
-webkit-border-radius: 0 0 5px 5px;
-moz-border-radius: 0 0 5px 5px;
border-radius: 0 0 5px 5px;
-webkit-transition: opacity .25s ease .1s;
-moz-transition: opacity .25s ease .1s;
-o-transition: opacity .25s ease .1s;
-ms-transition: opacity .25s ease .1s;
transition: opacity .25s ease .1s;
}
.menu li:hover > ul { opacity: 1; }
.menu ul li {
height: 0;
overflow: hidden;
padding: 0;
-webkit-transition: height .25s ease .1s;
-moz-transition: height .25s ease .1s;
-o-transition: height .25s ease .1s;
-ms-transition: height .25s ease .1s;
transition: height .25s ease .1s;
}
.menu li:hover > ul li {
height: 36px;
overflow: visible;
padding: 0;
}
.menu ul li a {
width: 145px;
padding: 4px 0 4px 10px;
margin: 0;
border: none;
border-bottom: 1px solid #4B0101;
}
.menu ul li:last-child a {
border: none;
}
.LoL
{
background: url(LoLicon.png) no-repeat 6px center;
}
.home
{
background: url(home.png) no-repeat 6px center;
}
.ssf2
{
background: url(SSF2.png) no-repeat 6px center;
}
.contact
{
background: url(contact.png) no-repeat 6px center;
}
.headlist
{
color:#ff9900;
}
.menu ul li:first-child a {
border-bottom: 3px solid #4B0101;
}
It's been 2 hours I'm searching so please help! :O

Answer 1

Margin: 0 auto; will not work with absolute positioning. Try removing position:absolute from the div and then it should work.
Here is the fiddle

Answer 2

If it must be absolutely positioned (thus meaning margin: auto won't work), then you can change the CSS to left: 50% and add margin-left: -295px;.
This will move the <div> 50% from the left, and then negatively bring it back by half of it's width, this leaving it in the middle.
http://jsbin.com/iJESEwe/1/edit?html,css,output