Hi Marcel,

First you must add a class to your menu item, to learn how you can do that please see this video.

Then you can go to Custom CSS area and style that button. That's it!

Extra: Here is an example that we used for the Restaurant demo:

/* Menu: Special button */
@media screen and (min-width: 768px) {
    .special-menu-button a{
        -webkit-box-shadow: 0 10px 30px 3px rgba(0,0,0,0.08);
        box-shadow: 0 10px 30px 3px rgba(0,0,0,0.08);
        -webkit-border-radius: 40px;
        -moz-border-radius: 40px;
        border-radius: 40px;
        padding: 4px 15px;
        background: #d09e5b;
        color: #fff !important;
        margin-left: -15px;
    }
    
    .special-menu-button a:after {
        background-color: transparent !important;
    }
}

Will set this ticket as solved from here.