Unable to generate different style for projected forecasted-data vs the original-data about plot HOT 2 CLOSED

package main

import (
	"image/color"
	"log"

	"golang.org/x/exp/rand"
	"gonum.org/v1/plot"
	"gonum.org/v1/plot/plotter"
	"gonum.org/v1/plot/vg"
)

func main() {
	rnd := rand.New(rand.NewSource(1))

	// randomPoints returns some random x, y points
	// with some interesting kind of trend.
	randomPoints := func(n int, x float64) plotter.XYs {
		pts := make(plotter.XYs, n)
		for i := range pts {
			pts[i].X = float64(i) + x
			pts[i].Y = 2*(float64(i)+x) + 3 + 10*rnd.Float64()
		}
		return pts
	}

	n := 100

	p := plot.New()
	p.Title.Text = "Data + Prediction"
	p.X.Label.Text = "X"
	p.Y.Label.Text = "Y"
	p.X.Min = 0
	p.X.Max = 100

	pts := randomPoints(n, 0)
	data, err := plotter.NewLine(pts[:80+1])
	if err != nil {
		log.Panic(err)
	}
	data.LineStyle.Color = color.RGBA{R: 255, A: 255}

	pred, err := plotter.NewLine(pts[80:])
	if err != nil {
		log.Panic(err)
	}
	pred.LineStyle.Color = color.RGBA{B: 255, A: 255}
	pred.LineStyle.Dashes = []vg.Length{1, 2, 1}

	p.Add(data, pred)
	p.Add(plotter.NewGrid())
	p.Legend.Add("data", data)
	p.Legend.Add("prediction", pred)

	err = p.Save(15*vg.Centimeter, 10*vg.Centimeter, "ooo.png")
	if err != nil {
		log.Fatal(err)
	}
}