Change the dark color of the header when it comes out in smaller screen

How do I change the dark color of the header when it comes out in smaller screen, I saw this functions:

.site-header.has-header {
    background-color: #000;
    position: relative;
}

I changed the color but the transparent effects and the sticky menu, go out…

Thank’s you :wink:

Hello,

Can you please provide a link to your website in order to let me inspect it?

Kind Regards, Roman.