initDefs = (svg) => {
const defs = svg.append("defs");
gradientIds.forEach((id, i) => {
const gradient = defs
.append("linearGradient")
.attr("id", id)
.attr("x1", "0%")
.attr("x2", "100%")
.attr("y1", "0%")
.attr("y2", "100%");
gradient
.append("stop")
.attr("class", "start")
.attr("offset", "0%")
.attr("stop-color", darkColors[i])
.attr("stop-opacity", 1);
gradient
.append("stop")
.attr("class", "end")
.attr("offset", "100%")
.attr("stop-color", uDarkColors[i])
.attr("stop-opacity", 1);
});
}