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CSS

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JavaScript

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HTML 

              
                <div class="container">
  <div class="pie-box">
    <div class="pie" id="clockPie">
      <div class="pie__segment" style="--value: 0; --over50: 0"></div>
      <!-- value 超過 50 就要把 over50 設為 1 -->
    </div>
  <div class="control">
    <button class="button" id="startBtn">start</button>
    <button class="button" id="cancelBtn" disabled>cancel</button>
  </div>
</div>
!

CSS 

              
                .pie {
  background: var(--remain-color, #639);
  border-radius: 100%;
  height: calc(var(--size, 200) * 1px);
  width: calc(var(--size, 200) * 1px);
  position: relative;
  /* overflow: hidden; */
  clip-path: circle(50%);
}
.pie__segment {
  --a: calc(var(--over50, 0) * -100%);
  --b: calc((1 + var(--over50, 0)) * 100%);
  /* clip-path: polygon(0 0, 100% 0, 100% 100%, 0 100%); */
  clip-path: polygon(var(--a) var(--a),var(--b) var(--a),var(--b) var(--b), var(--a) var(--b));
  /* 改使用剪裁多邊形 */
  height: 100%;
  position: absolute;
  width: 100%;
  transform: translate(0%, 50%) rotate( calc(var(--offset, 90)* 1deg));
  transform-origin: 100% 50%;
  transition: clip-path 0s;
}
.pie__segment:after,
.pie__segment:before {
  background: var(--pass-color, #f00); 
  content: '';
  position: absolute;
  height: 100%;
  width: 100%;
}
.pie__segment:before {
  --degrees: calc((var(--value,0)/100)*360);
  content: '';
  position: absolute;
  height: 100%;
  width: 100%;
  transform: translate(0, 100%) rotate( calc(var(--degrees) * 1deg));
  /* 因為 pie__segment 已經轉了90 度, 所以 translate 100% 會往左移 */
  transform-origin: 50% 0%;
  /* transition: transform 1s; */
}
.pie__segment:after {
  opacity: var(--over50, 0);
  /* transition-delay: 1s; */
}


* {
  box-sizing: border-box;
}
html, body{
  width: 100%;
  height: 100%;
}
body {
  background-color: #e0a0a0;
  display: flex;
  align-items: center ;
}
.container{
  width: 100%;
  /* height: 100%; */
}
.pie-box {
  --size: 200;
  --pass-color: #aa3333;
  --remain-color: #5555aa;
  height: calc(var(--size, 200) * 1px);
  width: calc(var(--size, 200) * 1px);
  margin: 0 auto;
}
.control{
  margin-top: calc((var(--size,200) / 10 )*1px);
  text-align: center;
}
.button {
  border: none;
  padding: 5px 10px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
}
!

JS 

              
                let timer;
const time = 10;
let timeLeft = time; //timeLeft in sec

window.addEventListener('DOMContentLoaded', (event)=>{
  startBtn.addEventListener('click', start);
  cancelBtn.addEventListener('click', cancel);
})

function updateBtnState(state){
  switch(state) {
    case 'start':
      startBtn.setAttribute("disabled", "disabled");
      cancelBtn.removeAttribute("disabled");
      break;
    case 'finish':
    case 'cancel':
      startBtn.removeAttribute("disabled");
      cancelBtn.setAttribute("disabled", "disabled");
      break;
    default:
      console.log("unknown state")
  }
}

function updatePie(percentage){
  // paint pie by percentage
  const pie = document.querySelector('.pie__segment') 
  pie.style.cssText = `--value: ${percentage}; --over50: ${percentage >= 50 ? 1 : 0}`; 
}

function start(event){
  if(this.disabled){
    return 
  }
  updateBtnState('start')
  console.log('click start')
  timer = setInterval(countDown, 1000)
}
function cancel(event){
  if(this.disabled){
    return 
  }
  clearInterval(timer);
  finish();
  console.log('click cancel')
}
function finish(){
  updateBtnState("finish");
  console.log("Finish!!!");
  timeLeft = time;
  updatePie(0);
}
function countDown(){
  if(--timeLeft < 0){
    finishTimer();
    return
  }
  console.log(timeLeft/time*100)
  updatePie(100 - timeLeft/time*100);
}
function finishTimer(){
  console.log("finish timer")
  clearInterval(timer);
  finish();
}
!
999px

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