everybody seems to use pixels to determine screen size of a device, but it is not a good practice anymore. You can use bootstrap to create a responsive website, but it will fail on full hd screens, because a lot of pixels, don't mean big screen anymore.
My example: on bigger screens, I don't want website to take the entire screen and on smaller screens I do. The easy solution is to use max-width, but it doesn't work if a device has a full hd screen, because it's small with a lot of pixels.