can't get rounded corners or transparency on my DIVs to show in IE9.

[Technetium]

In the CSS file, I have:
[php]#imageviewer
{
position: absolute;
top: 0;
left: 0;
margin-left: 50px;
margin-top: 50px;
background: #000000;
opacity: 0.8;
border: 2px solid #CCCCCC;
border-radius: 10px;
[/php]

This DIV shows up correctly in Firefox, but IE9 will have square corners and no transparency. I checked F12 and it tells me that IE9 is running in IE7 Standards Mode. If I change it to IE9 Standards, it will correctly show the DIV with rounded corners and transparency. Of course it reverts back to IE7 if I close the browser, and this has no effect on what would happen if other people were to view the page on their own browsers.

When I visit reliable sites like google, it will run in IE9 Standards. I cannot figure out how to get it to run in IE9 mode. At the top of my page, I have:

Is this the correct one to use? There are so many DOCTYPEs out there and it’s not really easy to figure out which one you need. I was also told to put this in the HEAD:

[Technetium]

I hit the PHP code by accident for the CSS… I would edit it but there doesn’t seem to be a button or link to edit posts. It looks like it cut off the bottom of the code. Here it is in normal code.

#imageviewer { position: absolute; top: 0; left: 0; margin-left: 50px; margin-top: 50px; background: #000000; opacity: 0.8; border: 2px solid #CCCCCC; border-radius: 10px; }