.mainmenu, .submenu {
    list-style: none;
    margin: 0;
    padding: 0;
}

    .mainmenu li, .submenu li {
        list-style: none;
    }

.mainmenu {
    display: flex;
    /*background: #f5f5f5;*/
}

    .mainmenu > li {
        position: relative;
        margin-right: 20px;
    }

        .mainmenu > li:last-child {
            margin-right: 0;
        }

        .mainmenu > li > a,
        .submenu > li > a {
            display: block;
            padding: 10px 20px;
            color: #333;
            text-decoration: none;
            white-space: nowrap;
        }

        .mainmenu > li > a {
            border: 1px solid purple;
            border-radius: 5px;
            background: #fff;
            transition: box-shadow 0.2s;
        }

            .mainmenu > li > a:hover,
            .submenu > li > a:hover {
                text-decoration: underline;
                text-underline-offset: 5px;
            }

.submenu {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background: #fff;
    min-width: 180px;
    z-index: 100;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.mainmenu > li.open > .submenu {
    display: block;
}

.mainmenu > li.active > a {
    text-decoration: underline;
    text-underline-offset: 5px;
    color: #111;
    font-weight: bold;
}