Help with making a layer hover over another layer

I have a website I am building using wordpress, and I am having a little trouble with the menu/logo. My menu is aligned to the right, and I want my logo on the left hand side. But the logo is pushing down the menu when I make the logo bigger. And because of that it is messing up the background texture of my header. what would be the way to make the image hover over the menu layer, or make the menu layer appear behind it, so it doesnt get pushed down when I make the logo bigger? Thanks in advance.

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Where to you want the menu actually to be? Assuming at the bottom, you could do this:

#headerMenu {position: relative;}
.main-navigation {position: absolute; bottom:0; right: 0;}

I want it to stay where it is, I just don’t want the logo that is on the left side to push the entire header down when it gets to where the invisible part of the menu is. I want it to float over the menu.

I just tried what you gave me and it looked like it worked. Thanks!