<style type="text/css">
#second {
border: 5px solid transparent;
}
</style>
Internet Explorer 7 supports transparent borders, but in IE6 the border becomes black.
<!--[if lt IE 7]>
<style type="text/css">
#third {
border-color: fuchsia;
filter:chroma(color=fuchsia);
}
</style>
<![endif]-->
Okay, this doesn't work that well :)