Too Long; Didn't Read
The viewport defines the area of the screen that the browser can render the content to. Viewport size is based on the width of the browser window, rather than the pixel density of the display. By setting the “width=device-width” in the meta viewport tag we instruct the page to match the screen width in device-independent pixels. This allows the page. to reflow content to match screen sizes, whether rendered on a small, medium or large screen.