specificity

I'm trying to understand CSS specificity, and have read all the info I can find online, but still cannot understand why in the below code, the #RedPlease ID doesn't take priority over h2 and make everything red. I thought ID selectors were more specific than elements (h2 below would fall under this correct?). I'm interested in the reasoning behind why the below example is working the way it is. Thanks for your help and your patience with the super basic nature of this question!

<div id="RedPlease">
	<h2>Header Two Why Are You Green?</h2>
    <p>This is a paragraph.  Why is my ID tag not making that header red?</p></div>
 
h2 { background-color: lime; }
#RedPlease { background-color: red; }