Responsive web design is an approach to web design in which a site is crafted to provide an optimal viewing experience—easy reading and navigation with a minimum of resizing, panning, and scrolling—across a wide range of devices (from desktop computer monitors to mobile phones).
The blog that you’re reading this article on is actually a responsive design! To see it in action, make the browser thinner and wider. You should see the layout magically adjust itself to more comfortably fit the new width of the browser.
Responsive web Design Testing Tools:
Related POST: What is Responsive Design and How to implement?