Margin top dropdown menu

My idea is

• Add a blank item to top of Dropdown Menu
• Use code to make this item invisible
• Use code to make Dropdown Transparent
• Use code to set Dropdown Items (from item 2, 3, 4...) background color

Add a blank item to top of Dropdown Menu, then

Don't remove any code in your current code then use this code in Custom CSS box

a.header-nav-folder-title:hover+div, .header-nav-folder-content {
    padding-top: 0 !important;
    background-color: Transparent !important;
}

div.header-nav-folder-content>div:first-child {
    visibility: hidden;
    opacity: 0;
}

div.header-nav-folder-content>div:not(:first-child) {
    background-color: var(--siteBackgroundColor);
    padding-left: 30px !important;
    padding-right: 30px !important;
}
div.header-nav-folder-content>div:nth-child(2) {
    padding-top: 10px !important;
}