.woocommerce-store-notice, 
p.demo_store {
    background-color: #000000 !important; /* Black banner */
    color: #ffffff !important; /* White text */
    font-weight: 700;
    text-align: center;
    padding: 12px 0;
}

.woocommerce-store-notice a {
    color: #ffffff !important; /* White link text */
    text-decoration: underline;
    font-weight: 700;
}