Custom CSS in Wordpress not working

[admin]

I've struggled with this problem with a while and still couldn't find the solution.
I've created custom CSS box for my posts in wordpress, but the thing is, it is not working. Box doesn't show up, no matter what I do.

Was hoping if someone could see what I am doing wrong.

Thanks

Style:

.square880x165 {
margin: 10px auto;
display: block;
width: 880px;
height: 165px;
padding: 20px;
position: relative;
float:left;
background-image: -webkit-gradient(linear, 50% 0%, 50% 100%, color-stop(0%, #aaaeaf), color-stop(100%, #689ecd));
background-image: -webkit-linear-gradient(#aaaeaf, #689ecd);
background-image: -moz-linear-gradient(#aaaeaf, #689ecd);
background-image: -o-linear-gradient(#aaaeaf, #689ecd);
background-image: -ms-linear-gradient(#aaaeaf, #689ecd);
background-image: linear-gradient(#aaaeaf, #689ecd);
-webkit-border-radius: 4px;
-moz-border-radius: 4px;
-ms-border-radius: 4px;
-o-border-radius: 4px;
border-radius: 4px;
-webkit-box-shadow: 0 1px 3px rgba(0,0,0,.35);
-moz-box-shadow: 0 1 3px rgba(0, 0, .35);
box-shadow: 0 1 3px rgba(0, 0, .35);
background: white;
-webkit-border-radius: 2px;
-moz-border-radius: 2px;
-ms-border-radius: 2px;
-o-border-radius: 2px;
border-radius: 2px;
bottom: 1px;
content: '';
left: 1px;
right: 1px;
top: 1px;

}

and HTML:

<div class="square880x165"><p>test</p></div>