@ganzheitlich You can upload the image to any image hosting site like https://imgur.com/ and share the URL here.
If you can’t share the URL, then, in this case, you can assign a custom CSS class name to the menu item you want to design. This article can walk you through the process: https://www.lockedownseo.com/add-css-classes-to-menu-items-in-wordpress
If you add the CSS class name menu-link to any item then you can write CSS like this I shared below to WordPress Dashboard > Appearance > Customize > Additional CSS field.
/* Change menu item background color on hover */
.home-link.menu-item:hover {
background: #ad6868 !important;
}
/* Change the text color of the menu item on hover */
.home-link.menu-item a:hover {
color: #000000 !important;
}
You can change the color codes from the above codes as you want.
Hope this helps! ??