Sorry,

Please use following css code.

.mobile-nav {

background-color: #000 !important; 

}

The color still hasn't changed on the menu background to black.

Hello,

Please use following css code to change the background of the mobile menu.

.mobile-nav {
color: #000; 
}

And unfortunately, you can not show login link in the mobile in modern style.

Please add login page to the menu item in Appearance -> Menus menu.

Then you will see the login menu in the desktop an mobile. 

Best regards,

How can I change the background color menu from blue to another color and the sign up button disappears on mobile view how can I prevent that from happening