It's Free, It's Fast, It Blocks Popups, It Has Tabs, Download Now.
http://www.mozilla.org/
Check your sites in it.
</end rant>
PS: It is the same thing Netscape minus the AOL stuff and not as many plug-ins so it is a smaller download and install.
I use external style sheets in all of my stuff without any problems, but you do need to leave the <body> tag blank or it overrides your stylesheet in some browsers.
Here is a typical one of mine,
body { color: white; font-size: 11px; font-family: Verdana, Arial, Helvetica, san-serif; background: #c99 url(background.jpg) 0px 0px; margin: 0px; padding: 0px }
a { color: white; text-decoration: none }
a:visited { color: white }