BorderRadius
data class BorderRadius(val topLeft: Length? = null, val topRight: Length? = null, val bottomRight: Length? = null, val bottomLeft: Length? = null)
Corner radii (border-radius) as four explicit corners.
Like Spacing, the uniform shorthand ({ "value", "unit" }) is accepted on the wire and expanded to all four corners on decode. Omitted corners stay null (CSS 0).