Banner image not filling page?

Site URL: https://www.harmonenterprises.com/webinar-mastering-evernote-v10

I have a solid color image uploaded as the banner image for the body of this index page (7.0 site). I cannot figure out why it isn't filling the full page. I have a spacer block below the button, and I want the green background to extend all the way to the bottom of the page. The footer information is in a different page, and I want that background to be white (as it is). But, as you can see, the green banner image isn't extending to the bottom of the spacer block that is in the main body page.

Any ideas why or how I can fix it? 

I've used this technique in multiple pages before and never had this issue so I'm stumped.

The uploaded banner image I'm using is 1000 x 1000 pixels:

Any ideas for me? Thanks in advance if you do.

@tuanphan Thanks for the code. I tried it and got an error message (see banner at top of screenshot). I'm guessing it's user error on my part, but I don't know CSS so don't know how to fix. I conceptually understand what you are suggesting though.

Never mind! Figured it out...I needed <style> tags. All fixed 🙂

Thank you.