Twenty eleven child theme Fix the position of search bar and menu

Hi all,

I’m completely new to wordpress and have read through the forums to do most of the stuff I needed on my site. However the one thing I just can’t get my head round or find info on is how to fix the search bar and main menu on my site so as you adjust the size of your browser window the menu just disappears off the side of the screen rather than auto adjusting.

my site is

https://www.confettitsunami.co.uk,

Thankyou