Size and Quality issue of logo in sticky navigation

Hello,

I'm building the website for my company.

https://ellipse-saffron-85rw.squarespace.com/tous-nos-evenements

pwd : sqbalboste

I integrated a sticky menu thanks to javascript. it's working correctly, but I'm having issue with the logo height and quality on the sticky menu only. I'm not a coder, a friend of mine gave me this sticky menu code. But I have basic CSS knowledge and understanding.

Sticky menu height is apparently based on the the logo png file height i'm using. Issue is that with the logo I'm using to define the height, logo is blury, I supposed because it's too small and does'nt has enough pixels to be detailed (I'm using a macbook pro retina)

I'm trying to solve this quality issue.

I guess using a bigger logo file, and defining the sticky menu height with CSS and not png size is the solution. but d'ont know how to do it.

If anyone can help me, would be appreciated !

Thanks you

Jonathan