CSS：畫鋸齒形邊的圓

鋸齒形邊的圓可以由十二個正三角形構成。

.circle {
  width: 80vh;
  height: 80vh;
  position: relative;
  background-color: #CCCCCC;
}

.triangle {
  position: absolute;
  left: 6.7%;
  top: 0;
  width: 86.6%;
  height: 75%;
  background-color: plum;
  clip-path: polygon(50% 0, 0 100%, 100% 100%);
  transform-origin: center 66.6%;
}

.triangle:nth-child(2) {
  transform: rotate(10deg);
}

.triangle:nth-child(3) {
  transform: rotate(20deg);
}

.triangle:nth-child(4) {
  transform: rotate(30deg);
}

.triangle:nth-child(5) {
  transform: rotate(40deg);
}

.triangle:nth-child(6) {
  transform: rotate(50deg);
}

.triangle:nth-child(7) {
  transform: rotate(60deg);
}

.triangle:nth-child(8) {
  transform: rotate(70deg);
}

.triangle:nth-child(9) {
  transform: rotate(80deg);
}

.triangle:nth-child(10) {
  transform: rotate(90deg);
}

.triangle:nth-child(11) {
  transform: rotate(100deg);
}

.triangle:nth-child(12) {
  transform: rotate(110deg);
}

<div class="circle">
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
  <div class="triangle"></div>
</div>

效果圖：