Sorry I should have been more specific. The viewport is merely the window of the browser itself where the website is rendered. The calculations given to devs reflects that area, and it does change if the user resizes their browser. But it doesn’t change if something is displayed on top.

It’s true that some temporary browser elements will display on top of the viewport, but these are things like alerts where it makes sense.

To have a permanent fixture that takes up space and then have the viewport lie to devs about the actual dimensions is really frustrating.