Change background of navigation to picture

Hi guys & gals,

I’m hoping someone can help me - I’ve been searching for an answer for ages but no luck!

I’d like to change the background of the navigation menu so it’s the same as the front page. Don’t think it looks very professional when it swaps to a block of colour. Here’s my site for reference (just started).

And The History of Excel: 34 Years of Magic for an example of what I’d like to achieve.

Thanks in advance,