@namespace a url(http://www.example.org/a);
@namespace b url(http://www.example.org/b);
div.green * { background-color : red }
div.testText * { display : block ; margin-bottom : 1em }
div.testText |* { background-color : lime }

<p>This html:p should NOT have a green background</p>
<elementA xmlns="http://www.example.org/a">This a:elementA element should
     NOT have a green background</elementA>
<elementB xmlns="http://www.example.org/b">This b:elementB should NOT have
     a green background</elementB>
<div class="green">
<p xmlns="">This p without declared namespace should  have a green background</p>
<elementA xmlns="">This elementA without declared namespace element should
     have a green background</elementA>
<elementB xmlns="">This elementB without declared namespace should have a
     green background</elementB>
</div>