Issue adding background image to header

Site URL: https://matthew-kern-drzz.squarespace.com/paintings-new

Hello, 

I am attempting to apply a background image to the header section of this website universally. For now I have just applied it to the specific page mentioned. I've had some success with the following code: 

#collection-6058d724f45e96664a810213 header#header {
    background-image: url(Image here);
    background-size: cover;
    background-position: center center;
    background-repeat: no-repeat;
}

However as you can see from the link: 

https://matthew-kern-drzz.squarespace.com/paintings-new

The image does not cover the entire section. I'd like it instead to look like this: 

Does anyone have a solution? 

Cheers, 

M. 

Hi. Looks fine here. Can you explain clearly?

Hi thanks for response. The question was answered on a different forum. Turns out the canvas was wrapped in  <div class="canvas"> with the following CSS: 

#canvas {
    max-width: 1200px;
    margin: 0px auto;
    padding: 75px;
}

Adding this CSS: 

#header{
    position: absolute;
    top: 0;
    right: 0;
    margin-bottom: 9px;
}

Resolved the issue.