Your web pages with fixed width of 800px may be fairly annoying to users with high-DPI displays. Mac Retina displays are perhaps the most recent and well known

Your web pages with fixed width of 800px may be fairly annoying to users with high-DPI displays. Mac Retina displays are perhaps the most recent and well known, but for years some people have had displays with DPI 50-200% higher than "normal", and for these people, your 800px decision looks like handcuffs. If you look back a dozen years you'll see a number of sites that instituted fixed-pixel-width layouts, then abandoned the approach as people bought more large, high-res displays. P.S.: Yes, some operating systems and browsers now zoom in a way that this doesn't matter so much, but not all, and not without downsides.