how can I make the menu corners rounder?

Hello again,

I have been trying to make menu corners rounder.

I've modified template_css.css line 691:

#nav li:hover > ul {
background:url(../images/topmenu_bg.png) no-repeat;
border-bottom:1px solid #7f7f7f;
-webkit-border-radius:5px;
-moz-border-radius:5px;
-o-border-radius:5px;
border-radius:5px;
}

And I put 15px instead:

#nav li:hover > ul {
background:url(../images/topmenu_bg.png) no-repeat;
border-bottom:1px solid #7f7f7f;
-webkit-border-radius:15px;
-moz-border-radius:15px;
-o-border-radius:15px;
border-radius:15px;
}

but only the corners in the lower border get rounder. I'm sending image to show what I mean.

My URL: cpcmetepec.com.mx/pruebas/

Thank you.

Susana

Edit this image:

templates/hot_business/images/topmenu_bg.png

undo that css