You have it backwards.
The styles cascade thru the (code indented) layers unless overridden by the layer
Body is the base
a Div or blockquote might establish a special grouping
then your P
So if you set Body, the rest inherit that unless you make a new declaration.
Usually, that is the only place I set line-height: (I also use the standard 1.2)
There are a few places I do use a different line-height
Code:
<h3 class="chapter> Chap title <br />Chap sub title</h3>
a bigger LH number spaces the lines apart