Logo and navigation, overlay!

Hello,

I am hoping someone can help me with some coding. I am using the theme Ample.

Firstly, I want to centre my logo within my navigation. Whilst doing this I want to overlay my logo by about 25px, so it is slightly overlapping my focus image at the top.

If this is possible and I can then create a sticky navigation and logo (to allow the page to slide underneath it) that would be even more amazing!!

Is there anyone that can help me do this please? I have added an image to make this clearer. (Image here!) Thank you so much in advance!

http://www.theardourcreative.com