Navigation drop down menu - 2 columns?

Site URL: https://sponge-seal-64fn.squarespace.com/config

Hi, I would like to put two columns for the drop down menu.

I tried to use the code from this thread but I can't make it work.

I used this code:

[href="/shop"]+.Header-nav-folder {
    column-count: 2;
}

Add to Home > Design > Custom CSS

[href="/ponuda2"]+.header-nav-folder-content {
    column-count: 2;
}

Thanks, @tuanphan!
This works with me. 

I got a question, how would you make a drop-down menu item, bold or hide. I am trying this one but it doesn't work (I am using 7.1)

a[href="/mega-menu"]+.header-nav-folder-content .header-nav-folder-item.header-nav-folder-item--external a:nth-child(5){
font-weight: bold;
}

  also this one is not working, nothing happens;

a[href="/mega-menu"]+.header-nav-folder-content a:nth-child(5){
font-weight: bold;
}

I would like the "Antioxidants" to bold and hide "Herbs"

Thank you!

I follow this but this is not working on mine: