Hi
1. In currently, you can only change the hover background color of those buttons. So you need to add the following custom CSS into Samsara options > Custom styles > CSS code, to change the initial color of the buttons.
.tools ul li a{background:#000;}
Just change the color value.
2. Generally, the background color of the drop menu is sync with the navigation bar color if you have changed it via Appearance > Customize, if you want to set the separate color for the drop menu, you need to add the following custom CSS.
#primary-menu ul ul{background-color:#fff;}
#primary-menu ul ul li a{color: #000;}
The second line is the link color of drop menu.
3. Unfortunately, it doesn’t support that layout on mobile in currently, and this is a customization issue (Exceed the support), maybe you need to customize some CSS for responsive.
4. Can you post a screenshot? Because I tried to reduce the window size of browser, it looks fine. What am I missing?
Thanks