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CSS

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HTML 

              
                <div class="container">
  <div class="progresscar">
    <span class="wheel"></span>
    <span class="wheel"></span>
  </div>
  <label class="debug-toggle-container" for="debug-toggle">
    <input type="checkbox" id="debug-toggle" /> debug
  </label>
  <header class="heading">
    <h1>Scroll down</h1>
  </header>

  <main class="content">
    <article class="article">
      <h2>An article</h2>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit? Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor</p>
      <p>Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem? Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit? Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor</p>
      <p>Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem? Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum?</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum? Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum?</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit? Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor</p>
      <p>Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem? Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit? Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor</p>
      <p>Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem? Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum?</p>
      <p>Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum? Lorem quasi magni placeat voluptates deserunt, eos ex, eum Quod molestiae odio fugit ad ullam Hic suscipit obcaecati nulla non maiores, qui. Ratione optio obcaecati error nihil deleniti Sit odit?</p>
      <p>Dolor tempora harum cum rerum sunt magnam! Est id iure repellat necessitatibus earum voluptates Quaerat libero rem cupiditate corporis repudiandae? Repellendus eaque quas laborum error labore Facilis sunt exercitationem dolor Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis Amet ipsa beatae harum voluptatem laudantium delectus? Suscipit in rerum culpa rerum harum totam illum! Similique nam officiis sit recusandae temporibus. Id officia reiciendis iusto neque iure hic. Delectus exercitationem?</p>
      <p>Consectetur delectus dolorem doloribus quisquam officiis earum Doloribus fuga cumque ipsa sint voluptatibus, similique Praesentium itaque quisquam officiis labore id? Architecto hic odit perspiciatis facilis officiis expedita, dolorum Dolore veritatis</p>
      <p>Sit nostrum sunt eligendi delectus quis? Facilis quos sapiente libero repellat rem. Culpa similique minima corporis laudantium est, quis Natus velit cumque eligendi amet rem. Similique voluptas rerum dignissimos laborum?</p>
      <p>Car picture is taken from <a href="https://www.carolenash.com/news/classic-car-news/detail/bullitt-mustang-to-be-restored-and-put-on-the-road-again">this website</a></p>
    </article>
  </main>
  <div class="ruler">
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
    <span></span>
  </div>
</div>
!

CSS 

              
                /* [number] means there's an explanation for that at the very bottom. */

:root {
  --π: 3.14159;
}

.progresscar {
  --car-width-px: calc(var(--car-width) * 1px);
  position: fixed;
  bottom: 0;
  left: 0;
  width: var(--car-width-px);
  height: calc(var(--car-width-px) / 3.2);
  background: url('progresscar.png') no-repeat center center;
  background-size: 100%;
  mix-blend-mode: soft-light;
  /* [1] */
  --road-length: calc(100vw - var(--car-width-px));
  transform: translateX(
    calc(var(--scroll-y-1) * var(--road-length))
  );
}

.wheel {
  --size: calc(var(--car-width) / 14);
  --size-px: calc(var(--size) * 1px);
  position: absolute;
  bottom: calc(var(--size-px) / 2);
  display: inline-block;
  width: var(--size-px);
  height: var(--size-px);
  background: url('progresscar-rim.png') no-repeat center center;
  background-size: 100%;
  /* [2] */
  --circumference: calc(var(--π) * var(--size));
  --road-length: calc(var(--vw) - var(--car-width));
  --rotations: calc(var(--road-length) / var(--circumference));
  transform: rotate(
    calc(1turn * var(--rotations) * var(--scroll-y-1))
  );
}

/* [3] */
.wheel:first-child {
  left: calc(var(--car-width-px) / 5.4);
}

/* [3] */
.wheel:last-child {
  right: calc(var(--car-width-px) / 7);
}

/* boilerplate */
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font: normal 100%/1.5 "Operator Mono", menlo, monaco, monospace;
}

.container {
  padding: 1em;
  transition: all .3s;
}

@media (min-width: 670px) {
  .container {
    width: 640px;
    margin: 0 auto;
    padding: 5em 0;
  }
}

/* debug mode */
.debug-toggle-container {
  position: fixed;
  top: 1em;
  right: 1em;
  padding: .5em;
  background: #FFFFFFEE;
  cursor: pointer;
}

.debug {
  width: 100%;
  padding: 5em;
  background-image: repeating-linear-gradient(
    90deg,
    transparent,
    transparent 1.8vw,
    rgba(0, 0, 0, .2) 2vw
  );
}

.debug .heading {
  font-size: 2em;
}

.debug .article {
  opacity: 0;
}

.debug .ruler {
  position: fixed;
  z-index: 0;
  bottom: calc(30% - 50px);
  left: 0;
  width: 100%;
  height: 50px;
}

.ruler span {
  --wheel-size: calc(var(--car-width) / 14);
  display: block;
  width: calc(var(--wheel-size) * var(--π) * 1px);
  height: 100%;
  float: left;
}

.ruler span:nth-child(even) {
  background: pink;
}

.ruler span:nth-child(odd) {
  background: black;
}

.debug .progresscar {
  bottom: 30%;
  mix-blend-mode: initial;
  z-index: 1;
}

.debug .wheel::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  width: 3px;
  height: 80px;
  transform: translateX(-50%);
  background: lime;
}

/*
 * Explanations
 *
 * [1] (L:17):
 * --scroll-y-1 property is provided by kicss.js
 * It's 0 when the page scroll is 0, and it's 1 when the page scroll reached the bottom.
 * Here we map scroll-y-1 to translateX.
 *
 *
 * [2] (L:34):
 * Rotation of each wheel
 * - wheel circumference: π * size (size = 2r)
 * - road length: viewport-width - car-width
 * - scroll-y-1: value between 0 and 1
 *
 * We need to use a custom absolute number for viewport-width, instead of 100vw,
 * because otherwise it can't be multiplied by 1turn
 *
 * To calculate how much rotation is needed, this formula is used:
 * 1turn * scroll-y-1 * (road-length / circumference)
 *
 * To put in human language:
 * For one full wheel rotation to happen, the car must move exactly as much
 * as the circumference of the wheel. This means page should be scrolled just
 * enough for the car to move exactly one-wheel-circumference forward.
 *
 *
 * [3] (L:43, L:48):
 * arbitrary positioning based on the car image used. 
 *
 *
 *
 * Credits:
 * Car picture source: https://www.carolenash.com/news/classic-car-news/detail/bullitt-mustang-to-be-restored-and-put-on-the-road-again
 */
!

JS 

              
                /*
 * An experimental mini library that I authored, called KICSS, is used
 * for communicating a few dynamic variables to CSS using custom properties.
 *
 * For more info, check:
 * - https://github.com/scriptype/kicss
 * - https://enes.in/kicss/
 *
 * Note that it's very premature and probably buggy at the moment.
 */
import { reportGlobals, reportVariable } from "https://enes.in/kicss/kicss.js"

reportGlobals({
  scroll: true
})

const { min } = Math
const innerWidth = () => window.innerWidth

reportVariable('--car-width', () => min(innerWidth() / 3, 600))
reportVariable('--vw', innerWidth)

/*
 * Debug controls
 */
const debugToggle = document.querySelector('#debug-toggle')
debugToggle.addEventListener('click', () => {
  document.body.classList.toggle('debug')
})
!
999px

Console