All of the websites I design, build and work on collaboratively are fully responsive, primarily using html, css, sass, js & jquery. Some projects require more heavy duty solutions and are built on technologies like .NET, node.js, C#, React, Vue, Angular and so on.
Some of the sites I've worked on over the years have stood out as great projects to show case, including intelliflo office, which is what I work on full time. It has over 350 pages, more than 150,000 users, a team of over 200 developers and of course my wonderful UI team colleagues whom I collaborate with to design, build and improve all aspects of UX. Others go way back to the first responsive websites I made, for my very first client! (It's still up to this day, proving the longevity of well written, clean html and css - despite all the fuss about React and js frameworks!)