How can I Enable Responsiveness?

I’ve tried modifying several elements through CSS to have a max-width of 100% with no joy. Seems like this should be easy.
My only “solution” is to limit the width to 480 and assume people will rotate their phones (not idea is it??)

https://sleepsense2014.franksdesigns.com/sample-newsletter-2/

https://www.ads-software.com/plugins/facebook-comments-plugin/