Personal Portfolio: My background image is not opening up. What am I doing wrong?

I am trying to cover the page with a background image here:

I am using the same specs recommended on this website:

What might I be doing wrong?

Also the background image in my first attempt is not showing:

I could see the image before. Has the editor been updated in some way? Thank you for the help.

Remember to set your html selector in css as 100% height.

It doesn’t seem to be working still.

Oh, and the <div class="bg"></div> after the body. That’s the layer that contains the background.

I would like the title to stay in the center of the background image always regardless of the size of the browser window. Is there a way to do this?