What is the "id" of new paragraph ?

Answer 1

I talk about DOM

Answer 2

I guess you are talking about HTML and the <p> tag. It does not have any ID until you specify it with an id-attribute like this:
<p id="myPID">my P text</p>

You can then use it in CSS like:
#myPID{
baclground-color: green;
}

Answer 3

That is what i was talking about too.
https://www.w3schools.com/js/js_htmldom_nodes.asp