If you control both the HTML and CSS, I'd suggest switching to using ID's on all the divs needed for the rounded corner.
CSS
#d1 {
background: #CFFEB6 url('tr.gif') no-repeat top right;
}
#d2 {
background: url('br.gif') no-repeat bottom right;
}
#d3 {
background: url('bl.gif') no-repeat bottom left;
}
#d4 {
padding: 10px;
}
HTML
<div id="d1"><div id="d2"><div id="d3"><div id="d4">
<div class='button'><a href='#'>Test</a></div>
</div></div></div></div>