Statically center div on screen (no JS) - html

Question

What I already have:
.modal-m1
{
background-image: url(../images/bg-greyout.png);
background-repeat: repeat;
display: table;
top: 0;
left: 0;
width: 100%;
height: 100%;
position: fixed;
margin: 0;
padding: 0;
z-index: 1;
}
.modal-m1 .modal-m2
{
display: table-cell;
vertical-align: middle;
}
.dialogbox
{
margin: 0 auto;
background-color: #F6F6F6;
-webkit-border-radius: 20px;
-moz-border-radius: 20px;
border-radius: 20px;
-webkit-box-shadow: #666 3px 3px 5px;
-moz-box-shadow: #666 3px 3px 5px;
box-shadow: #666 3px 3px 20px;
padding: 20px;
}
.mydialogbox
{
width: 400px;
}
<div class="modal-m1">
<div class="modal-m2">
<div class="dialogbox mydialogbox">
... CONTENT IS HERE ......
</div>
</div>
</div>
Everything is okay on that stage. You may test it on snippet.
Now I want to put several dialog boxes to different pages. I'm trying to reuse the code and for that reason I'm trying to extract modal-m1, modal-m2 and dialogbox to ASP.NET user control. mydialogbox must become a nested div inside of dialogbox. But dialogbox ignores width: 400px in this case. Is there any workaround?
In other words, I want my markup to be:
<div class="modal-m1">
<div class="modal-m2">
<div class="dialogbox">
<div class="mydialogbox">
... CONTENT IS HERE ......
</div>
</div>
</div>
</div>
Is it possible?

Answer 1

if I undestood..
your html can be like this:
<div class="modal-m1">
<div class="modal-m2">
<div class="dialogbox ">
<div class="mydialogbox">
<div>CONTENT IS HERE ......</div>
</div>
</div>
</div>
</div>
and you want put width only for .mydialogbox
.modal-m1 .modal-m2
{
display: table-cell;
vertical-align: middle;
text-align:center; /*add*/
}
.dialogbox
{
margin: 0 auto;
background-color: #F6F6F6;
-webkit-border-radius: 20px;
-moz-border-radius: 20px;
border-radius: 20px;
-webkit-box-shadow: #666 3px 3px 5px;
-moz-box-shadow: #666 3px 3px 5px;
box-shadow: #666 3px 3px 20px;
padding: 20px;
display:inline-block; /*change*/
}
.mydialogbox
{
width: 400px;
text-align:left
}
is this?