@media (max-width: 600px) {
    #categories-list li a {
        display: block;
        min-width: 140px;
        text-align: left;
        padding-left: 16px;
        line-height: 28px;
        font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
        color: #fff;
        background:  lightslategray;
        text-decoration: none;
    }

    .background-gray {
        background-color: lightslategray;
    }
}