.red { background-color : red }
p:not(:nth-last-of-type(3)) { background-color : lime }
dl > *:not(:nth-last-of-type(3n+1)) { background-color : lime }

<p>This paragraph should NOT have green background</p>
<address>This address should NOT have green background</address>
<p class="red">This paragraph should have green background</p>
<p class="red">This paragraph should have green background</p>
<dl>
  <dt class="red">First definition term that should have green background</dt>
    <dd class="red">First definition</dd>
  <dt class="red">Second definition term that should have green background</dt>
    <dd class="red">Second definition</dd>
  <dt>Third definition term</dt>
    <dd>Third definition</dd>
  <dt class="red">Fourth definition term that should have green background</dt>
    <dd class="red">Fourth definition</dd>
  <dt class="red">Fifth definition term that should have green background</dt>
    <dd class="red">Fifth definition</dd>
  <dt>Sixth definition term</dt>
    <dd>Sixth definition</dd>
</dl>