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CSS

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HTML 

              
                <div class="container">
	<section class="section-1">
		<h1>Animate on scroll</h1>
		<p>Let's see if we can can animate on scroll with intersection observer</p>
	</section>
	<section class="section-2">
		<h2 class="section-title">Steps to make this</h2>
		<div class="grid card-grid intersection-sentry">
			<div class="card">
				<h3 class="card-title">First Design with no js</h3>
				<p class="card-text">First thing we are going to do is make the page with no js</p>
			</div>
			<div class="card">
				<h3 class="card-title">Then figure out positions</h3>
				<p class="card-text">Now we decide how we want to animate and set the position with CSS transform, opacity and transition</p>
			</div>
			<div class="card">
				<h3 class="card-title">Finally do the JS</h3>
				<p class="card-text">Add an intersection observer to update the custom properties to make it animate</p>
			</div>
		</div>
	</section>
	<section class="section-3">
		<div class="grid grid-row intersection-sentry">
			<div class="grid-row-content">
				<h2 class="section-title">Possible things that could be done to improve</h2>
				<p>Could watch for a no-js class on the body and reset everything into the correct position and maybe add a pollyfill for intersection observer</p>
			</div>
			<img class="grid-row-image" src="https://images.unsplash.com/photo-1536098561742-ca998e48cbcc?crop=entropy&cs=srgb&fm=jpg&ixid=MnwxNDU4OXwwfDF8cmFuZG9tfHx8fHx8fHx8MTY1MDE2ODQ1NQ&ixlib=rb-1.2.1&q=85" alt="">
		</div>
	</section>
	<section class="section-4">
		<h2>That's it for now</h2>
		<p>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Voluptate sit dolores officia beatae suscipit voluptates veritatis cumque repellendus eaque, praesentium, odit vero, harum non illum debitis officiis dolorem veniam ipsam.</p>
	</section>
</div>
!

CSS 

              
                @use postcss-preset-env;
:root {
	--color-1: #171123;
	--color-2: #372248;
	--color-3: #414770;
	--color-4: #5B85AA;
	--color-5: #F46036;
	--white: #fff;
	--black: #212427;
	--bg: var(--color-2);
	--base-fs: 1rem;
	--fs: var(--base-fs);
}

:is(h1, h2, h3) {
		font-size: var(--fs);
		text-align: center;
		line-height: 1;
}

h1 {
	--fs: calc(var(--base-fs) * 2.5);
}

h2 {
	--fs: calc(var(--base-fs) * 2);
}

h3 {
	--fs: calc(var(--base-fs) * 1.5);
}

section {
	color: var(--white);
	background: var(--bg);
	min-height: 80vh;
	font-size: var(--fs);
	padding: 1.5em;
	display: grid;
	place-content: center;
}
.
.section-1 p {
	text-align: center;
	margin-top: 3em;
}

.section-2 {
	--bg: var(--color-3);
}

.section-3 {
	--bg: var(--color-4);
}

.section-4 {
	--bg: var(--color-5);
}

.grid {
	display: grid;
		grid-template-columns: repeat(auto-fit, minmax(min(250px, 100%), 1fr));
}

.card-grid {
	--translate-init: translate(0, 75px);
	--translate: var(--translate-init);
	--opacity: 0;

	gap: 1.25em;
	margin-top: 3em;
	transform: var(--translate);
	transition: var(--transition);
	opacity: var(--opacity);
	width: 100%;
  max-width: 80vw;
}


@media(min-width: 650px) {
	.card:last-of-type {
		grid-column: span 2;		
	}
}

@media(min-width: 988px) {
	.card:last-of-type {
		grid-column: auto;
	}
}

.card {
	text-align: var(--text-align);
	line-height: 1.5;
	background: var(--white);
	color: var(--color-1);
	padding: 1.5em;
	border-radius: 1em;
	box-shadow: 1px 4px 8px var(--color-1);
}

.grid-row {
	--translate-init: translate(60px, 0);
	--translate: var(--translate-init);
	--opacity: 0;
	max-width: 1440px;
	width: 100%;
	place-content: center;
	gap: 2em; 
}

.grid-row-content {
	width: 100%;
	max-width: 60ch;
	text-align: var(--text-align);
	align-self: center;
}

.grid-row-image {
	max-width: 400px;
	width: 100%;
	transform: var(--translate);
	transition: var(--transition, 0);
	opacity: var(--opacity, 0);
	justify-self: center;
}

.section-4 p {
	max-width: 100ch;
}

/* disable animation for people who have the reduced motion in accessibility settings. */
@media (prefers-reduced-motion: reduce) {
	*,
	*::before,
	*::after {
		transition: 0 !important;
		transform: translate(0) !important;
		opacity: 1 !important;
	}
}
!

JS 

              
                const options = {
	rootMargin: "100%"
};

const handleIntersect = (entries, observer) => {
	entries.forEach((entry) => {
		const target = entry.target;
		if (entry.isIntersecting) {
			target.style.setProperty("--transition", "all .75s");
			target.style.setProperty("--opacity", "1");
			target.style.setProperty("--translate", "translate(0)");
		} else {
			target.style.setProperty("--transition", "0");
			target.style.setProperty("--translate", "var(--translate-init)");
			target.style.setProperty("--opacity", "0");
		}
	});
};
const intersectorSentries = document.querySelectorAll(".intersection-sentry");

const observer = new IntersectionObserver(handleIntersect, options);
intersectorSentries.forEach((sentry) => observer.observe(sentry));
!
999px

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