original

max-width: 586px;
height: auto;
border: 1px solid #fff;
padding: 4px;
background: #f0f0f0;
box-shadow: 0px 0px 1px #cecece;
-moz-box-shadow: 0px 0px 1px #cecece;
-webkit-box-shadow: 0px 0px 1px #cecece;

new code

.post-content .alignnone, .post-content .alignleft, .post-content .alignright, .post-content .aligncenter {
background: none
border-color: none
border-style: none;
border-width: 0;
box-shadow: none;
}