CSS code for home page image isn't working

Full disclosure, I am a novice with code.

I'm trying to establish a full background image on ONLY my homepage, but the following code shows up as a header text, and the image isn't affected at all:

.Header{
  postion: fixed;
  z-index: 1000;
  width: 100%
}

I uploaded an image as a banner on the home page. I've tried to input this code on the actual page, as well as the custom CSS settings sitewide, and no change.

Page in progress EDIT: https://alpaca-cheetah-7pzw.squarespace.com/homepage

What am I doing wrong?

@ashdan87 You should share site url to check code.

9 minutes ago, tuanphan said:

@ashdan87 You should share site url to check code.

Done, thank you 🙂

@ashdan87 your site is private. Please setup up password & then share url