body {
}

h3 {
    background-color: #eee;
    color: #444;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    text-align: left;
    border: none;
    outline: none;
    transition: 0.4s;
}

    h3.active, h3:hover {
        background-color: #ddd;
    }