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HTML

              
                <div class="gallery">
	<ul class="cards">
		<li>0</li>
		<li>1</li>
		<li>2</li>
		<li>3</li>
		<li>4</li>
		<li>5</li>
		<li>6</li>
		<li>7</li>
		<li>8</li>
		<li>9</li>
		<li>10</li>
		<li>11</li>
		<li>12</li>
		<li>13</li>
		<li>14</li>
		<li>15</li>
		<li>16</li>
		<li>17</li>
		<li>18</li>
		<li>19</li>
		<li>20</li>
		<li>21</li>
		<li>22</li>
		<li>23</li>
		<li>24</li>
		<li>25</li>
		<li>26</li>
		<li>27</li>
		<li>28</li>
		<li>29</li>
		<li>30</li>
	</ul>
	<div class="actions">
		<button class="prev">Prev</button>
		<button class="next">Next</button>
	</div>
</div>
              
            
!

CSS

              
                * {
	box-sizing: border-box;
}
body {
	background: #111;
	min-height: 100vh;
	padding: 0;
	margin: 0;
}
.gallery {
	position: absolute;
	width: 100%;
	height: 100vh;
	overflow: hidden;
}

.cards {
	position: absolute;
	width: 14rem;
	height: 18rem;
	top: 40%;
	left: 50%;
	transform: translate(-50%, -50%);
}

.cards li {
	list-style: none;
	padding: 0;
	margin: 0;
	width: 14rem;
	height: 18rem;
	text-align: center;
	line-height: 18rem;
	font-size: 2rem;
	font-family: sans-serif;
	background-color: #9d7cce;
	position: absolute;
	top: 0;
	left: 0;
	border-radius: 0.8rem;
}

.actions {
	position: absolute;
	bottom: 25px;
	left: 50%;
	transform: translateX(-50%);
}

button {
  display:inline-block;
  outline: none;
  border: none;
  padding: 8px 14px;
  background: #414141;
  background-image: -webkit-linear-gradient(top, #575757, #414141);
  background-image: -moz-linear-gradient(top, #575757, #414141);
  background-image: -ms-linear-gradient(top, #575757, #414141);
  background-image: -o-linear-gradient(top, #575757, #414141);
  background-image: linear-gradient(to bottom, #575757, #414141);
  text-shadow: 0px 1px 0px #414141;
  -webkit-box-shadow: 0px 1px 0px 414141;
  -moz-box-shadow: 0px 1px 0px 414141;
  box-shadow: 0px 1px 0px 414141;
  color: #ffffff;
  text-decoration: none;
  margin: 0 auto 10px;
  -webkit-border-radius: 4;
  -moz-border-radius: 4;
  border-radius: 4px;
  padding: 12px 25px;
  font-family: "Signika Negative", sans-serif;
  text-transform: uppercase;
  font-weight: 600;
  cursor: pointer;
  font-size: 13px;
  line-height: 18px;
}

button:hover {
  background: #57a818;
  background-image: -webkit-linear-gradient(top, #57a818, #4d9916);
  background-image: -moz-linear-gradient(top, #57a818, #4d9916);
  background-image: -ms-linear-gradient(top, #57a818, #4d9916);
  background-image: -o-linear-gradient(top, #57a818, #4d9916);
  background-image: linear-gradient(to bottom, #57a818, #4d9916);
  text-shadow: 0px 1px 0px #32610e;
  -webkit-box-shadow: 0px 1px 0px fefefe;
  -moz-box-shadow: 0px 1px 0px fefefe;
  box-shadow: 0px 1px 0px fefefe;
  color: #ffffff;
  text-decoration: none;
}

button {
  font-size: 20px;
  font-weight: 400;
}

a {
  color: #88ce02;
  text-decoration: none;
}
a:hover {
  text-decoration: underline;
}
              
            
!

JS

              
                gsap.registerPlugin(ScrollTrigger);

let iteration = 0; // gets iterated when we scroll all the way to the end or start and wraps around - allows us to smoothly continue the playhead scrubbing in the correct direction.

const spacing = 0.1,    // spacing of the cards (stagger)
	snap = gsap.utils.snap(spacing), // we'll use this to snap the playhead on the seamlessLoop
	cards = gsap.utils.toArray('.cards li'),
	seamlessLoop = buildSeamlessLoop(cards, spacing),
	scrub = gsap.to(seamlessLoop, { // we reuse this tween to smoothly scrub the playhead on the seamlessLoop
		totalTime: 0,
		duration: 0.5,
		ease: "power3",
		paused: true
	}),
	trigger = ScrollTrigger.create({
		start: 0,
		onUpdate(self) {
			if (self.progress === 1 && self.direction > 0 && !self.wrapping) {
				wrapForward(self);
			} else if (self.progress < 1e-5 && self.direction < 0 && !self.wrapping) {
				wrapBackward(self);
			} else {
        scrub.vars.totalTime = snap((iteration + self.progress) * seamlessLoop.duration());
				scrub.invalidate().restart(); // to improve performance, we just invalidate and restart the same tween. No need for overwrites or creating a new tween on each update.
				self.wrapping = false;
			}
		},
		end: "+=3000",
		pin: ".gallery"
	});

function wrapForward(trigger) { // when the ScrollTrigger reaches the end, loop back to the beginning seamlessly
	iteration++;
	trigger.wrapping = true;
	trigger.scroll(trigger.start + 1);
}

function wrapBackward(trigger) { // when the ScrollTrigger reaches the start again (in reverse), loop back to the end seamlessly
	iteration--;
	if (iteration < 0) { // to keep the playhead from stopping at the beginning, we jump ahead 10 iterations
		iteration = 9;
		seamlessLoop.totalTime(seamlessLoop.totalTime() + seamlessLoop.duration() * 10);
    scrub.pause(); // otherwise it may update the totalTime right before the trigger updates, making the starting value different than what we just set above. 
	}
	trigger.wrapping = true;
	trigger.scroll(trigger.end - 1);
}

function scrubTo(totalTime) { // moves the scroll position to the place that corresponds to the totalTime value of the seamlessLoop, and wraps if necessary.
	let progress = (totalTime - seamlessLoop.duration() * iteration) / seamlessLoop.duration();
	if (progress > 1) {
		wrapForward(trigger);
	} else if (progress < 0) {
		wrapBackward(trigger);
	} else {
		trigger.scroll(trigger.start + progress * (trigger.end - trigger.start));
	}
}

document.querySelector(".next").addEventListener("click", () => scrubTo(scrub.vars.totalTime + spacing));
document.querySelector(".prev").addEventListener("click", () => scrubTo(scrub.vars.totalTime - spacing));




function buildSeamlessLoop(items, spacing) {
	let overlap = Math.ceil(1 / spacing), // number of EXTRA animations on either side of the start/end to accommodate the seamless looping
		startTime = items.length * spacing + 0.5, // the time on the rawSequence at which we'll start the seamless loop
		loopTime = (items.length + overlap) * spacing + 1, // the spot at the end where we loop back to the startTime 
		rawSequence = gsap.timeline({paused: true}), // this is where all the "real" animations live
		seamlessLoop = gsap.timeline({ // this merely scrubs the playhead of the rawSequence so that it appears to seamlessly loop
			paused: true,
			repeat: -1, // to accommodate infinite scrolling/looping
			onRepeat() { // works around a super rare edge case bug that's fixed GSAP 3.6.1
				this._time === this._dur && (this._tTime += this._dur - 0.01);
			}
		}),
		l = items.length + overlap * 2,
		time = 0,
		i, index, item;

	// set initial state of items
	gsap.set(items, {xPercent: 400, opacity: 0,	scale: 0});

	// now loop through and create all the animations in a staggered fashion. Remember, we must create EXTRA animations at the end to accommodate the seamless looping.
	for (i = 0; i < l; i++) {
		index = i % items.length;
		item = items[index];
		time = i * spacing;
		rawSequence.fromTo(item, {scale: 0, opacity: 0}, {scale: 1, opacity: 1, zIndex: 100, duration: 0.5, yoyo: true, repeat: 1, ease: "power1.in", immediateRender: false}, time)
		           .fromTo(item, {xPercent: 400}, {xPercent: -400, duration: 1, ease: "none", immediateRender: false}, time);
		i <= items.length && seamlessLoop.add("label" + i, time); // we don't really need these, but if you wanted to jump to key spots using labels, here ya go.
	}
	
	// here's where we set up the scrubbing of the playhead to make it appear seamless. 
	rawSequence.time(startTime);
	seamlessLoop.to(rawSequence, {
		time: loopTime,
		duration: loopTime - startTime,
		ease: "none"
	}).fromTo(rawSequence, {time: overlap * spacing + 1}, {
		time: startTime,
		duration: startTime - (overlap * spacing + 1),
		immediateRender: false,
		ease: "none"
	});
	return seamlessLoop;
}

              
            
!
999px

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