The rem unit is relative to the root—or the html—element. That means that we can define a single font size on the html element and define all rem units to be a percentage of that.
Anything that’s fixed and unresponsive isn’t web design anymore, it’s something else. If you don’t embrace the inherent fluidity of the web, you’re not a web designer, you’re something else. Web design is responsive design, Responsive Web Design is web design, done right.