Help making my theme responsive

Hello! I need help making my theme more responsive. My website is https://www.amanda-mackay.com . I am using the theme named Expositio and I would like to add auto-scaling capabilities to it so it looks nice on as many screens as possible!

I have already tried the advice given on this site without any success ??

https://colorlabsproject.com/tutorials/make-your-wordpress-theme-responsive/

I also tried installing tablepress to see if I could change it that way and it could not detect any tables.

Any help would be super appreciated!

Thanks ~ Amanda