I bought a used monitor a while back and did what everyone tells you to do first: pull up an online "dead pixel test" and cycle through some solid colors before deciding whether to keep it. It worked, but afterward I was curious why every single one of these tools looks identical — same handful of colors, same full-bleed look, no ads-covered corners, nothing fancy. So I built my own version to see what's actually involved, and it turns out almost none of the interesting work is in the colors. It's in getting a <div> to actually, reliably, cover the entire physical screen.
The colors are chosen, not decorative
The color grid isn't nine random swatches — each one is picked to isolate a specific kind of pixel failure:
const testModes = [
{ key: "red", style: { background: "#FF0000" } },
