These properties specify the gradient colouration of an edge's line:

https://js.cytoscape.org/#style/gradient

interface Gradient {
    line-gradient-stop-colors?: PropertyValueEdge<string>[];
    line-gradient-stop-positions?: PropertyValueEdge<number>[];
}

Properties

line-gradient-stop-colors?: PropertyValueEdge<string>[]

The colors of the gradient stops.

line-gradient-stop-positions?: PropertyValueEdge<number>[]

The positions of the gradient stops. If not specified (or invalid), the stops will divide equally.