A single slider drives every panel so you can compare quality and cost at the
same blur radius. The value is a Gaussian standard deviation in CSS pixels —
the same thing CSS filter: blur() takes — so the CSS panel is the
ground truth and every WebGL panel is calibrated to match it. The focus is on
techniques that stay cheap as the radius grows — the naïve approach's cost scales
with radius (or radius²), while the good ones don't.