a[href ^= 'http']:not([href *= 'html5rocks.']) {
background: transparent url(data:image/png;base64,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) no-repeat center right;
padding-right: 16px;
}
<p>Here is some text and an <a href="http://google.com">external link</a>, check out the little arrow graphic!
<p>Again, <a href="http://www.html5rocks.com/">links within our domain</a> appear as normal.