You can switch your browser to full-screen mode by pressing the
F11 key on your keyboard. However, not all users know this keyboard shortcut so it can be helpful in some cases to put a dedicated button on your webpage that allows to user to switch to full screen mode.
Modern desktop browsers support the Fullscreen API that allows entering to and exit from full-screen mode.
requestFullscreen() method on an element (and not on document) to put the element into fullscreen.