add preferred source style

.jnews-custom-preferred-source {
     margin : 30px 0;
}

.jnews-custom-preferred-source-button {
    display: inline-block;
    padding: 10px 16px;
    border: 1px solid #ddd;
    border-radius: 4px;
    text-decoration: none;
    font-weight: 600;
}