Best Practice for Positioning elements in html/css

Question

Sometimes I get so immersed in complex nested <div>s, that I forget the simple basics!

Suppose I have a web page where I want to position a blog post title about 45% down from the top of the page.
Nothing above the title, no images, no nothing, just empty space.

What's the best practice for creating that space?

My first though was:

<h1 style="margin-top: 12em;">Title here</h1>

(Not trying to use exact measurement. I just wanted to emphasize a large amount of room)

Answer 1

use vh for percent of window height:

<h1 style="margin-top: 45vh;">Title here</h1>