Each pair of overlapping circles blends via a genuine PDF blend mode (ExtGState /BM, ISO 32000-1 ยง11.3.5) - real compositing math, not an approximation. (docs/html-css-support.md#filters-and-blend-modes)
normal (baseline) mix-blend-mode: normal | multiply mix-blend-mode: multiply | screen mix-blend-mode: screen | difference mix-blend-mode: difference |