Why is my site header layout and theme malfunctioning?

[treebeard]

I am having several issues with layout. For some reason, the header(?) on my site has split the "cart," "create account," and "login" buttons into 3 lines, which makes everything look pretty jenky.  URL is here:

www.slngrow.com

It also no longer centers the slideshow on my homepage, and the featured products used to be bottom aligned... Also, when you visit the site on mobile, the main menu is automatically open, which never used to be the case.

The only thing I recently tried to do was split a dropdown menu... I did not get very far (am not a coder), and hence, to my knowledge nothing was saved.  

However, I now get this error message when trying to customize (fix!) the theme: 

The following error was found in assets/theme.scss.liquid

Invalid CSS after " }": expected "}", was "" at 2010

If anyone has any thoughts, I'm getting desperate!  

Many thanks.