JSFiddle - React, Tailwind, and code Playground

HTML

<div id="status-display">
    <div id="status-display-content">
    </div>
  </div>

  <div id="timer"></div>
  <div id="calculation-result"></div>

CSS

#status-display {
      background-color: #000;
      color: green;
      font: 111px Arial, sans-serif;
      width: 150px;
      height: 150px;
      border-radius: 21%;
      text-align: center;
      line-height: 150px;
    }

    #timer {
      width: 150px;
      text-align: center;
      font: 15px Arial, sans-serif;
    }

    #status-display-content {
      transition: opacity 1s
    }

    #calculation-result {
      margin-top: 1em;
    }

JavaScript

(function() {
      let startTimeOfProgram = performance.now(),
      timer = 3, 
      element = $("#status-display-content"),
      elementTimer = $("#timer");

      setInterval(() => { elementTimer.html((Math.round((performance.now() - startTimeOfProgram) / 10) / 100).toFixed(2)) }, 33);

      function updateState() {
        element.html(timer--).css({ transition: "none" }).css({ opacity: 1 });
        if (timer < 0) timer = 3;

        // need to be next cycle because cannot change
        // transition and have it animated all in the same cycle
        setTimeout(function() {
          element.css({ transition: "opacity 1s" }).css({ opacity: 0 }).on("transitionend", () => { updateState(); element.off("transitionend"); });
        }, 0);
      }

      updateState();


      function binaryLength(n) {
        return n.toString(2).length;
      }

      const occasionalSleeper = (function() {
        let lastSleepingTime = performance.now();

        return function() {
          if (performance.now() - lastSleepingTime > 33) {
            lastSleepingTime = performance.now();
            return new Promise(resolve => setTimeout(resolve, 0));
          } else {
            return Promise.resolve();
          }
        }
      }());

      async function asyncBigIntFactorial(n) {       
        let start = performance.now();

        n = BigInt(n);
        if (n <= 1n) return 1n;

        let result = 1n;
        for (let i = 2n; i <= n; i++) {
          await occasionalSleeper();
          result *= i;
        }
        console.log("Time taken", (performance.now() - start) / 1000);
        return result;
      }

      let startTimeOfComputation;

      setTimeout(function() {
        let startTimeOfComputation = performance.now();
        asyncBigIntFactorial(60000).then(result => {
          $("#calculation-result")
          .html(`Number of digits of answer in binary: ${binaryLength(result)}<br>Time it took: ${Math.round((performance.now() -...