15. doughnut chart

Let's create a doughnut chart in CSS.

1. radius: 50px
2. thickness: 10px
3. color: #f44336

The percentage should be able to set by CSS variable --percentage.

For example, to create a doughnut chart with 20%:

<div class="piechart" style="--percentage:20%"></div>

A doughnut chart with 75%:

<div class="piechart" style="--percentage:75%"></div>