I spent more time on this than I should have, and haven't tested in IE for obvious reasons. That being said, it's pretty much identical.
a.boxclose{
float:right;
margin-top:-30px;
margin-right:-30px;
cursor:pointer;
color: #fff;
border: 1px solid #AEAEAE;
border-radius: 30px;
background: #605F61;
font-size: 31px;
font-weight: bold;
display: inline-block;
line-height: 0px;
padding: 11px 3px;
}
.boxclose:before {
content: "×";
}