Have you ever seen one of those websites that look exactly the same on desktop and mobile and wonder why they would build it like that? In the new age of web development, why would someone not leverage the responsiveness provided by the latest HTML and CSS versions? This could happen to anyone; we have all the right breakpoints defined and are using media queries as expected, but nothing happens. This is usually because we forgot to include the viewport, the meta tag; including the meta tag for viewport fixes all our problems:

<meta name="viewport" content="width=device-width, initial-scale=1">

The viewport is basically the total viewable area for a user, which will be smaller in a mobile and larger in a desktop; the meta tag defines how the browser should render the website, based on the size of the viewport.