OptionalcolorDefault #e2e8f0.
OptionallevelsInteger 1..64 evenly spaced strictly inside yMin..yMax (default 12), or explicit raw-Y heights.
Optionalopacity0..1, default 0.85.
OptionalshowDefault false.
OptionalwidthVisual weight, not CSS px: hairline alpha x (0.75 + 0.15 x min(width, 4)). Default 1.5.
Height isolines traced on the rendered surface triangles (ChartGPU
contourscontract).