Project: color
Task (challenging): When click `.lch-wheel .wheel` color:
- change `.lch-wheel` background color to lch color with h from `.lch-wheel .wheel` angle, lightness 50 , chroma 50
- add a block (class `block`) in the `.lch-wheel` if it does not exist, and set its center at the clicked point
  - `.block` width and height is less than or equal 12px