As the number of people using their phones to access the internet grew, mobile design became the most important factor. Ethan Marcotte, a smart and determined web designer, revolutionized the way mobile website design was done in 2010. He advocated that instead of establishing a separate mobile site, the same content be used in multiple layouts and designs depending on screen size. The term "responsive design" was coined around this time.
We still utilize HTML and CSS on a technical level, so it's more of a conceptual shift. The fundamental advantage of Responsive Design is content parity, which means that the website looks the same everywhere.
