Custom CSS works on every page EXCEPT for the home page!

My template is Nuevo. My website is homecomfortsolutionsboise.com
Password is: Mnbb77
I found code that fixes the header to the top of the screen so as you scroll the nav bar is always accessible.
Here's the code I'm using:

Any ideas why it's not working on the front page?Any work arounds?
Is it because of the banner image?
Thanks for any help!

@haydenshapiro Use this code

   .Header {
       position: fixed !important;
       left: 0 !important;
       right: 0 !important;
       top: 0 !important;
       z-index: 999 !important;
   }

Tuan, you rule! Thank you!