No, websites use CSS for styling and layout, basically how elements should look, behave and how they are placed in relation to each other, CSS can query the browser for screen width and adjust the view in real time.

As a result, if you resize your browser, it may switch to a taller display style, which is what you want on mobile devices.

Note: there are many reasons you wouldn’t want to check for device type, this is why display width is used.