Remove right sidebar from mobile and tablets

Hi

I found several topics in which the following css was provided to remove the sidebar on tablet/mobile view -

@media (max-width: 768px) {
#right-sidebar {
display: none;
}
}

I added the css to the additional css field in the customizer, purched cache but the sidebar is still present on mobiles.

This is a URL from ne of the posts on the site where the sidebar should have been removed by the css - https://www.lovingmeow.com/what-smells-do-cats-hate/

Thanks,