<style type="text/css">
   .foo {
        -moz-border-radius: 100px;
        -webkit-border-radius: 100px;
         border-radius: 100px !important;
         width:200px;
         height:200px;
         background: #F00;
         overflow: hidden !important;
         position: fixed;
    }
</style>

<div class="foo"><iframe height="200px" width="200px"
src="http://maps.google.nl/maps?hl=nl&q=Arnhem+(Arnhem)&ie=UTF8&t=&z=9&iwloc=B&output=embed"></iframe></div>