Bug fix in highchart -- 2

Job ID: 33839933

Budget: ₹1,500 – ₹12,500 INR

Tasks

1. display plotband. Reference: [Plot bands and plot lines | Highcharts](https://www.highcharts.com/docs/chart-concepts/plot-bands-and-plot-lines)
2. plotband color alternates between gray and white

Currently:
screenshot-2022-06-03-06-32-15-original.png

Desired:
screenshot-2022-06-03-06-32-15-target.png

Link to sample project: https://mega.nz/file/4wwWRJpK#2Bb9ZLjbrypvRFLG3-XacijmDMkRX_5J4ANzxI4xwZo

Here's how to run the sample project:

1. cd into project dir `highcharts-plotband-src`
2. run a local server with `python3 -m http.server 8000 --bind 127.0.0.1`
3. Go to `http://127.0.0.1:8000/` in browser to make sure it's running properly

Thank you!
Related categories: CSS HTML5 Highcharts