Hi Jawad,
Thanks for reaching out.
If you are trying to hide the WooCommerce Store Notice for the whole site, you can disable the option for it from Appearance > Customize > WooCommerce > Store Notice as shown in the given screenshot.

But if you want the notice to be hidden only on these two given URLs, you need to add the !important to custom CSS code.
.page-id-20887 p.woocommerce-store-notice.demo_store
{
display: none !important;
}
Please remember that the above code will work if copied as it is and doesn’t conflict with any existing style.
Please note that the code provided serves only as a guide to help you get started custom coding on your own if there’s no option offered in our theme or the products we bundle.
We really do not provide support for custom codes that means we can’t fix it in case it conflicts with something on your site nor will we enhance it.
Thanks