How do I change the drop down menu colour background to light grey on my homestartpage without changing the whole background to grey?

How do I change the drop down menu colour background to light grey on my homestartpage without changing the whole background to grey?
I talked to a squarespace worker that said it had to be coded. Also where do I insert it?

Best regards
Maria

Can you share link to your site? I can take a look

Thank you so much! Here is the link and the password is "test" https://vibraphone-smilodon-r49f.squarespace.com/config/settings/site-visibility

place in custom css

 #topNav nav .folder-collection ul li a {
   background-color:#F4F4F4;
 }

Thank you so much! And where do I put the costume css? How do I insert it to the homepage? 

2 hours ago, mariasoerensen said:

Thank you so much! Here is the link and the password is "test" https://vibraphone-smilodon-r49f.squarespace.com/config/settings/site-visibility

No such website. Can you check url?

Sorry - here! https://mariasoerensen.squarespace.com/config/

It has to work on the mobile device also with the colors, so if there are a better solution im in for that, thanks!

Add to Home > Design > Custom CSS

.homepage .header-nav-folder-content {
    background: gray !important;
}

Thank you so much! It worked!!!

Can you also help me with this? I need the mobile device menu to be grey - this colour  hsl(43, 4%, 65%)  

right now its all white like in the photo

You can't see the menu because the text is white, but i hope you understand 

2 hours ago, mariasoerensen said:

You can't see the menu because the text is white, but i hope you understand 

Add to Home > Design > Custom CSS

.header-menu-bg.theme-bg--primary {
    background: gray !important;
}

I think you can also change this in Home > Design > Color?