JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="menu">
    <li><a href="#">Главная</a></li>
    <li><a href="#s1">Галерея</a>
        <ul class="submenu">
            <li><a href="#">Submenu a</a>
                <ul class="submenu">
            
                </ul>
            </li>
            <li><a href="#">Submenu b</a></li>
            <li><a href="#">Submenu c</a></li>
            <li><a href="#">Submenu d</a></li>
            <li><a href="#">Submenu e</a></li>
            <li><a href="#">Submenu f</a></li>
            <li><a href="#">Submenu g</a></li>
            <li><a href="#">Submenu h</a></li>
        </ul>
    </li>
    <li class="active"><a href="#s2">Файлы</a>
        <ul class="submenu">
            <li><a href="#">Submenu a</a></li>
            <li><a href="#">Submenu b</a></li>
            <li><a href="#">Submenu c</a></li>
            <li><a href="#">Submenu d</a></li>
            <li><a href="#">Submenu e</a></li>
            <li><a href="#">Submenu f</a></li>
            <li><a href="#">Submenu g</a></li>
            <li><a href="#">Submenu h</a></li>
        </ul>
    </li>
    <li><a href="#">Блог</a>
        <ul class="submenu">
            <li><a href="#">Submenu a</a></li>
            <li><a href="#">Submenu b</a></li>
            <li><a href="#">Submenu c</a></li>
            <li><a href="#">Submenu d</a></li>
            <li><a href="#">Submenu e</a></li>
            <li><a href="#">Submenu f</a></li>
            <li><a href="#">Submenu g</a></li>
            <li><a href="#">Submenu h</a></li>
        </ul>
    </li>
</ul>

CSS

/* general styles */
.menu, .menu ul {
    list-style: none;
    padding: 0;
    margin: 0;
}
.menu {
    height: 58px;
}
.menu li {
    background: -moz-linear-gradient(#292929, #252525);
    background: -ms-linear-gradient(#292929, #252525);
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #292929), color-stop(100%, #252525));
    background: -webkit-linear-gradient(#292929, #252525);
    background: -o-linear-gradient(#292929, #252525);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#292929', endColorstr='#252525');
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr='#292929', endColorstr='#252525')";
    background: linear-gradient(#292929, #252525);

    border-bottom: 2px solid #181818;
    border-top: 2px solid #303030;
    min-width: 160px;
}
.menu > li {
    display: block;
    float: left;
    position: relative;
}
.menu > li:first-child {
    border-radius: 5px 0 0;
}
.menu a {
    border-left: 3px solid rgba(0, 0, 0, 0);
    color: #808080;
    display: block;
    font-family: 'Lucida Console';
    font-size: 18px;
    line-height: 54px;
    padding: 0 25px;
    text-decoration: none;
    text-transform: uppercase;
}

/* onhover styles */
.menu li:hover {
    background-color: #1c1c1c;
    background: -moz-linear-gradient(#1c1c1c, #1b1b1b);
    background: -ms-linear-gradient(#1c1c1c, #1b1b1b);
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, #1c1c1c), color-stop(100%, #1b1b1b));
    background: -webkit-linear-gradient(#1c1c1c, #1b1b1b);
    background: -o-linear-gradient(#1c1c1c, #1b1b1b);
    filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#1c1c1c', endColorstr='#1b1b1b');
    -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr='#1c1c1c', endColorstr='#1b1b1b')";
    background: linear-gradient(#1c1c1c, #1b1b1b);

    border-bottom: 2px solid #222222;
    border-top: 2px solid #1B1B1B;
}
.menu li:hover > a {
 ...