Harris background and navigation issues

Hi all! 

New at coding so super grateful for all and any help! 

Firstly I am having trouble running the background image across the whole screen on the homepage with css. It's ending where that spark of light is and then repeating again in the background is that makes sense (image attached). I am trying to get it to be full screen and just can't seem to figure it out! This is the code I have

#collection-5ed0ed77ef385f4344feab85 .overflow-wrapper {
    background: url(https://static1.squarespace.com/static/5ed0e60285c7174bb45402cb/t/5ed8ee744a80dc4a5c04232b/1591275125424/bg7.png) !important;
}

Also, the navigation is stacking on someone else's screen (second image) Anyone know what I can do to force it to stay in a line? I probably sound like a total dunce but I am trying really hard to learn so thankyou in advance for any tips 🙂

Q1. add

background-repeat: no-repeat;

Q2. Can you share link to your site?