Project: color
Task (challenging): - default `.wheel` angle (h)  is 0
- add a whiteness vertical range (class `w`) in the `.hwb-wheel`
  - default value is 0
  - change whiteness range to update `.hwb-wheel` background color
- add a blackness vertical range (class `b`) in the `.hwb-wheel`
  - default value is 0
  - change blackness range to update `.hwb-wheel` background color