Responsive web design is the practice of building a website suitable to work on every device and every screen size, no matter how large or small, mobile or desktop.
Responsive web design is focused around providing an intuitive and gratifying experience for everyone.
Responsive web design makes your web page look good on all devices.
Responsive web design uses only HTML and CSS.
It is called responsive web design when you use CSS and HTML to resize, hide, shrink, enlarge, or move the content to make it look good on any screen.
Pages optimized for a variety of devices must include a meta viewport tag in the head of the document.
A meta viewport tag gives the browser instructions on how to control the page's dimensions and scaling.
<meta name="viewport" content="width=device-width, initial-scale=1">
Using the meta viewport value
width=device-width instructs the page to match the screen's width in device-independent pixels. This allows the page to reflow content to match different screen sizes, whether rendered on a small mobile phone or a large desktop monitor.
Some browsers keep the page's width constant when rotating to landscape mode, and zoom rather than reflow to fill the screen. Adding the attribute
initial-scale=1 instructs browsers to establish a 1:1 relationship between CSS pixels and device-independent pixels regardless of device orientation, and allows the page to take advantage of the full landscape width.