validClassName doesn't like camelCase class names.

[pdebruic]

plot/src/style.js

Line 417 in e2749e8

const validClassName =

validClassName.test('myNewClassName') fails.

[mbostock]

CSS class name selectors are case-insensitive, so consider using mynewclassname instead. But we should make this validation case-insensitive since it is a valid name.