The number of mobile users accessing the web is growing rapidly and the concept of Mobile First is directed to websites that should first of all be designed for mobile users. And not until then for desktop computers. I have not seen the term “Green website” yet, but if you don’t need to power up your desktop computer to have a nice experience and get the information – we are looking at a greener design.
Mobile First refers to the whole concept of designing for smaller screens as well as bigger screens. Is your essential information accessible and easy to navigate on an iPhone, tablet computer or a 24 inch desktop screen?
Responsive design is an answer to this request when it comes to graphic design of your website. A responsive design will know the size of your screen and adapt its layout according to your screen size, making sure the visitor have an easy access to the information.
Here is some elaborated information on the subjects: