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HTML

              
                - let cats = {
- 	'Tiger': {
- 		name: 'Panthera tigris', 
- 		code: '1501705388883-4ed8a543392c', 
- 		desc: 'tiger in the water'
- 	}, 
- 	'Lion': {
- 		name: 'Panthera leo', 
- 		code: '1519066629447-267fffa62d4b', 
- 		desc: 'lion and lioness resting on a rock in the sun'
- 	}, 
- 	'Leopard': {
- 		name: 'Panthera pardus', 
- 		code: '1566489564594-f2163930c034', 
- 		desc: 'blue-eyed leopard resting high up with its head on its front paws'
- 	}, 
- 	'Jaguar': {
- 		name: 'Panthera onca', 
- 		code: '1601544359642-c76c4f7c3221', 
- 		desc: 'jaguar closeup'
- 	}, 
- 	'Snow leopard': {
- 		name: 'Panthera uncia', 
- 		code: '1689847190291-f8e0823f13ab', 
-			desc: 'snow leopard lying low on some rocks, its fur blending in perfecty'
- 	}, 
- 	'Cheetah': {
- 		name: 'Acinonyx jubatus', 
- 		code: '1693702366986-cbfbd1cf0450', 
- 		desc: 'cheetah in the grass at dusk'
- 	}, 
- 	'Cougar': {
- 		name: 'Puma concolor', 
- 		code: '1661004527094-07d861089aed', 
- 		desc: 'cougar walking through the snow'
- 	}
- };
- let e = Object.entries(cats), n = e.length;
- let m = 15;

- function rand(max, min, prc = 2)
	- return +(min + (max - min)*Math.random()).toFixed(2)

section(style=`--n: ${n}; --k: 0`)
	- for(let i = 0 ; i < n; i++)
		- let v = e[i][1];
		article(style=`--i: ${i}; --a: ${rand(m, -1*m)}deg`)
			h2 #{e[i][0]}
			em #{v.name}
			img(src=`https://images.unsplash.com/photo-${v.code}?w=400` alt=v.desc)
	div
		button(aria-label='previous' data-inc='-1')
		button(aria-label='next' data-inc='1')
              
            
!

CSS

              
                $t: .8s;

/* register these two so they can be transitioned */
/* index of previous top item during the animation
 * after another has been selected */
@property --p {
	syntax: '<number>';
	initial-value: 0;
	inherits: true
}
/* animated index of top item from previous to current */
@property --v {
	syntax: '<number>';
	initial-value: 0;
	inherits: true
}

* { margin: 0 } /* poor man's reset */
/* grid everything! */
html, body, section, article, button { display: grid }
/* full viewport height container for stack section */
html { min-height: 100% }
body { background: #070410 }

section {
	/* set previous top item index to current top index
	 * 0s duration delayed transition ensures switch happens 
	 * after the switching top item transtion */
	--p: var(--k);
	/* abs of difference between current & previous top item indices
	 * 0 if not during animation, 
	 * 1 during animation not between two ends, 
	 * n - 1 > 1 (if n > 2) during animation from one end to another */
	--abs-p: abs(var(--k) - var(--p));
	/* animation from one end of the n > 2 length list to another?
	 * 0 if no, 1 if yes */
	--end: clamp(0, var(--abs-p) - 1, 1);
	/* direction we're going in given by 
	 * sign of difference between current & previous top item indices
	 * -1 backwards, 1 forwards, 0 no animation;
	 * switch sign IF we're going from an end to another */
	--dir: calc((1 - 2*var(--end))*sign(var(--k) - var(--p)));
	/*  forward direction flag: 0 backwards, 1 forwards */
	--fwd: calc(.5*(1 + var(--dir)));
	/* set animated value of top item index to current top index
	 * a transition ensures switch doesn't happen instantly */
	--v: var(--k);
	/* absolute value of difference between animated & previous top index */
	--abs-v: abs(var(--v) - var(--p));
	/* animation progress as a decimal value */
	--prg: calc(var(--abs-v)/(1 - var(--end) + var(--end)*(var(--n) - 1)));
	/* bigger space between the two columns (image stack & all else) */
	grid-gap: .5em 4em;
	grid-template: /* 4 row, 2 col grid */
		repeat(2, max-content) 1fr max-content/ 
		max-content 1fr;
	place-self: center;
	color: #f1f5f9;
	font: 1em poppins, sans-serif;
	counter-reset: k calc(1 + var(--k)) n var(--n);
	/* transition previous & animated top item indices 
	 * so they don't change instantly like the current one */
	transition: --p 0s $t, --v $t;
	
	/* counter & binomial name faded */
	&::before, em { color: RGB(from currentColor r g b/ .6) }
	
	&::before { /* counter */
		grid-area: 1/ 2; /* all grid areas need to be set manually */
		content: counter(k) '/' counter(n)
	}
	
	/* this ridiculousness needed for Chrome without flag */
	/* for reference
	 * https://css-tricks.com/using-absolute-value-sign-rounding-and-modulo-in-css-today/ */
	@supports not (scale: Abs(-2)) {
		--abs-p: max(var(--k) - var(--p), var(--p) - var(--k));
		--abs-v: max(var(--v) - var(--p), var(--p) - var(--v))
	}
	
	@supports not (scale: Sign(-2)) {
		--dir: clamp(-1, (var(--k) - var(--p))*100000, 1)
	}
}

article {
	/* absolute value difference between 
	 * currently top item index and current item index */
	--abs-top: abs(var(--k) - var(--i));
	/* not top item if the absoute value difference ≥ 1
	 * top if the difference is 0 */
	--not-top: min(1, var(--abs-top));
	/* top flag is the negation */
	--top: calc(1 - var(--not-top));
	/* difference between moving image index which is 
	 * previous top item index --p if going backwards, 
	 * current top item index --k if going forwards 
	 * and current item index --i */
	--val-mov: ((1 - var(--fwd))*var(--p) + var(--fwd)*var(--k) - var(--i));
	--abs-mov: abs(var(--val-mov));
	/* not moving image if the absoute value difference > 1
	 * moving image if the difference is 0 */
	--not-mov: min(1, var(--abs-mov));
	/* moving flag is the negation */
	--mov: calc(1 - var(--not-mov));
	grid-area: 1/ 1/ -1/ -1; /* stack to occupy entire parent grid */
	grid-template: subgrid/ subgrid; /* and inherit template */
	/* debatable whether z-index is the best way 
	 * maybe CSS 3D transforms would be a better idea */
	/* depends on number of items, its own index and top item index */
	z-index: mod(calc(var(--n) - 1 + var(--i) - var(--k)), var(--n));
	/* transition z-index */
	transition: z-index $t cubic-bezier(1, -.9, 0, 1.9);
	
	/* this ridiculousness needed for Chrome without flag */
	@supports not (scale: Abs(-2)) {
		--abs-top: max(var(--k) - var(--i), var(--i) - var(--k));
		--abs-mov: max(var(--val-mov), -1*var(--val-mov));
	}
}

h2, em {
	/* fade out and slide down when not top item anymore,
	 * delayed fade in and slide up when becoming top item */
	translate: 0 calc(var(--not-top)*1lh);
	opacity: var(--top);
	transition: .5*$t calc(var(--top)*.5*#{$t});
	transition-property: translate, opacity
}

/* need to specify grid-area for all */
h2 { grid-area: 2/ 2 }
em { grid-area: 3/ 2 }

img {
	/* value that grows from 0 to 1, then goes back to 0 
	 * during the switching top items transition */
	--sin: sin(var(--prg)*.5turn);
	grid-area: 1/ 1/ -1; /* occupy entire first column */
	/* slight glow effect */
	border: solid 2px rgba(82, 82, 122, .5);
	/* whatever, maybe better ways for setting dims */
	height: 13em;
	aspect-ratio: 1;
	object-fit: cover; /* fill with no distortion */
	border-radius: .75em;
	/* slide just moving image out & back in */
	translate: calc(-150%*var(--mov)*sqrt(var(--sin)));
	/* random rotation, but not during slide out & back in transition */
	rotate: calc((1 - var(--sin))*var(--a))
}

div { /* button wrapper */
	display: flex;
	gap: 2em;
	grid-area: 4/ 2;
	/* prevent button clicks during animation */
	z-index: calc((1 - min(1, var(--abs-p)))*var(--n))
}

button { /* prettify button */
	--sgn: -1;
	--prc: calc(var(--hov, 0)*100%);
	--c: color-mix(in hsl, #818cf8 var(--prc), #52527a);
	border: none;
	width: 1lh;
	aspect-ratio: 1;
	border-radius: 50%;
	background: RGB(from var(--c) r g b/ .2);
	color: color-mix(in hsl, #818cf8 var(--prc), currentcolor);
	font: 900 2em/ 1.5 sans-serif;
	transition: .3s ease-out;
	transition-property: background-color, color;
	
	&::before { /* arrow, SVG likely better, whatever */
		place-self: center;
		border: solid 2px;
		border-width: 2px 2px 0 0;
		width: 35%;
		aspect-ratio: 1;
		translate: calc(var(--sgn)*-15%);
		rotate: 45deg;
		scale: var(--sgn);
		content: ''
	}
	
	&[data-inc='1'] { --sgn: 1; }
	&:is(:hover, :focus) { --hov: 1 }
}
              
            
!

JS

              
                /* all the JS does is update current top item index */
const S = document.querySelector('section').style /* wrapper style */, 
			N = +S.getPropertyValue('--n') /* number of items */;

let k = +S.getPropertyValue('--k') /* idx of current top item */;

addEventListener('click', e => {
	let v = +e.target.dataset.inc /* value (±1) to change top idx by */;
	if(v) S.setProperty('--k', k = ((k + v + N)%N))
})
              
            
!
999px

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