p { background-color : red ; border : thick solid red ; padding : 1em }
p.t1 { background-color : lime }
p.t2 { border : thick solid green }

div { background: green; color: white; }
div.teST { background: red; color: yellow; }
div.te { background: red; color: yellow; }
div.st { background: red; color: yellow; }
div.te.st { background: red; color: yellow; }

<p class="t1 t2">This paragraph
should have a green background and a green thick solid border because
it carries both classes t1 and t2.</p>

<div class="test">This line
should be green.</div>