Is it possible to implement responsive design with most, if not all of the changes in CSS as opposed to HTML?

The scenario is that we are using a CMS third party product that hosts about 5-6 sites, and a lot of shared components are used throughout the sites.

Given our specific implementation and customization of the product, it's feasible to apply/load specific CSS for a given site, but it's harder to make changes to the HTML/components, since they are re-used on many of the sites.

Our team is looking to implement responsive design on just one of the websites, not all of them, so, without taking into consideration implementation details and just as a feasibility question, would it be possible to fully implement responsive web design using CSS only, and not using a mobile-first or responsive framework, which would require modifying the HTML to accommodate their responsive classes?

I'm not an expert in web design, but from what I've seen so far is that in responsive design, the bulk of the implementation is with CSS Media queries, but can it be done 100%, and not rely on JS for any of the responsive design features?

Thank you