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HTML

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CSS

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CSS Base

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JavaScript

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HTML 

              
                <div class="no-support" data-support="css-trig-fns"><p>🚨 Your browser does not support the CSS Trigonometric Functions. Therefore, this demo will not work properly. Please try Safari 15.4, Firefox 108, or Chrome 111.</p></div>

<form data-has-support="at-property" method="">
	<label for="enable_animation">
		<input type="checkbox" name="enable_animation" id="enable_animation" checked />
		Auto-rotate
	</label>
	<label for="show_debug">
		<input type="checkbox" name="show_debug" id="show_debug" />
		Show Debug Lines
	</label>
</form>

<div class="wrapper">
	<div id="visual" data-countchildren>
		<span class="dot"></span>
		<span class="dot"></span>
		<span class="dot"></span>
		<span class="dot"></span>
		<span class="dot"></span>
	</div>
</div>

<div id="controls" data-show-when-has-support="css-trig-fns">
	<button data-trigger="add">Add dot</button>
	<button data-trigger="remove">Remove dot</button>
</div>

<footer>
	<p>Demo for <a href="https://web.dev/css-trig-functions/" target="_top">https://web.dev/css-trig-functions/</a></p>
</footer>
!

CSS 

              
                @layer base, demo, demosupport;

/* Register --angle. That way we can transition and animate it 😎 */
@property --angle {
	syntax: '<angle>';
	initial-value: 0deg;
	inherits: true;
}
/* Initial value for browsers that don’t support @property */
:root {
	--angle: 0deg;
}

/* Keyframes that animates the --angle value */
@keyframes adjust-angle {
	to {
		--angle: 360deg;
	}
}

/* Enable animation when checkbox is checked */
:root {
	animation: adjust-angle linear 20s infinite paused;
}
:root:has(#enable_animation:checked) {
	animation-play-state: running;
}

/* The colored dots */
.dot {
	/* Spread the dots evenly over the circle.
	   We do this by dividing 360deg by the number of children.
       E.g. 360 degrees / 3 children = 120 degrees between each child element.	
	*/
	--offset-per-child: calc(360deg / (var(--nth-siblings) + 1));
	
	/* Each child will that offset into account, based its index.
	   E.g. - the 1st out of 3 children gets offset by 0 x 120deg = 0deg
	        - the 2nd out of 3 children gets offset by 1 x 120deg = 120deg
	        - the 3rd out of 3 children gets offset by 2 x 120deg = 240deg
	*/
	--angle-offset: calc(var(--nth-child) * var(--offset-per-child));
	
	/* Make it round */
	display: block;
	width: var(--tracksize);
	aspect-ratio: 1;
	border-radius: 50%;
	
	/* Color it, giving each color a different hue based on the --angle-offset */
	background: hsl(var(--angle-offset) 100% 50%);
	border: 1px solid #333;
	
	/* Center it */
	position: absolute;
	left: calc(50% - (var(--tracksize) / 2));
	top: calc(50% - (var(--tracksize) / 2));
	
	/* Adjust its position based on the --angle, while also taking the --angle-offset into account */
	translate: calc(cos((var(--angle) + var(--angle-offset))) * var(--radius))
		       calc(sin((var(--angle) + var(--angle-offset))) * var(--radius) * -1);
	
	/* Other things */
	pointer-events: none;
}


















@layer demo {
	@layer visual {
		/* The visualization */
		#visual {
			/* Dimensions of the visualization */
			--radius: 20vmin;
			--tracksize: 5vmin;

			/* Make it a circle, based on the dimensions */
			width: calc(var(--radius) * 2 + var(--tracksize));
			aspect-ratio: 1;
			border-radius: 50%;
			border: var(--tracksize) solid transparent;

			/* Some generic positioning stuff */
			margin: 0 auto;
			position: relative;
		}

		#visual {
			border-color: #e0e0e0;
		}

		/* Inject a dot at the center of the visualization */
		#visual::after {
			content: '';
			--size: calc(var(--tracksize) / 2);

			/* Make it round */
			display: block;
			width: var(--size);
			aspect-ratio: 1;
			border-radius: 50%;

			/* Put it in the center */
			position: absolute;
			left: calc(50% - (var(--size) / 2));
			top: calc(50% - (var(--size) / 2));
			z-index: 2;

			/* Make it black */
			background: #333;
		}
	}
	
	@layer debug {
		/* Draw debug lines for the red dot */
		:root:has(#show_debug:checked) .dot:nth-last-child(1)::before,
		:root:has(#show_debug:checked) .dot:nth-last-child(1)::after {
			/* Inject it */
			content: '';
			display: block;

			/* Color it */
			background: hsl(var(--angle-offset) 100% 50%);

			/* Position it */
			position: absolute;
			left: calc(50%);
			top: calc(50%);
			z-index: -1;

			transform-origin: 0 0;
		}

		:root:has(#show_debug:checked) .dot:nth-last-child(1)::before {
			width: var(--radius);
			height: 2px;

			/* Draw line on horizontal axis*/
			transform: 
				/* Adjust size based on cos() of angle */
				scaleX(cos(calc(var(--angle) + var(--angle-offset))))
				/* Move back so that it goes into the center of the dot */
				translate(-100%, -50%)
				/* Move back so that it appears on X axis instead of on the dot itself */
				translateY(calc(sin((var(--angle) + var(--angle-offset))) * var(--radius)))
			;
		}

		:root:has(#show_debug:checked) .dot:nth-last-child(1)::after {
			width: 2px;
			height: var(--radius);

			/* Draw line on vertical axis*/
			transform: 
				/* Adjust size based on sin() of angle */
				scaleY(sin(calc((var(--angle) + var(--angle-offset)) * -1)))
				/* Move back so that it goes into the center of the dot */
				translate(-50%, -100%)
			;
		}
	}
}


@layer demosupport {
	@layer layout {
		label, #controls, form {
			text-align: center;
		}
	}	
}

/* Non-demo styles below */
@layer base {
	@layer reset {
		* {
			box-sizing: border-box;
		}
		body {
			margin: 0;
			padding: 0;
		}
		html, body {
			height: 100%;
		}
	}
	@layer layout {
		html {
			max-width: 84ch;
			padding: 3rem 2rem;
			margin: auto;
		}
		body {
			display: grid;
			place-content: safe center;
			gap: 3rem;
		}

		html {
			--font-sans: system-ui,-apple-system,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif,Segoe UI,Roboto,Ubuntu,Cantarell,Noto Sans,sans-serif;
			--font-serif: ui-serif,serif;
			--font-mono: Dank Mono,Operator Mono,Inconsolata,Fira Mono,ui-monospace,SF Mono,Monaco,Droid Sans Mono,Source Code Pro,monospace;
		}
		body {
			font-family: var(--font-sans);
		}
		pre, code {
			font-family: var(--font-mono);
			font-size: 0.8rem;
		}
		input, button {
			font-family: inherit;
		}
		
		a,
		a:visited {
			color: blue;
		}
		
		h2 {
			margin-top: 2em;
		}

		summary {
			cursor: pointer;
		}

		dd + dt {
			margin-top: 0.5em;
		}

		button {
			cursor: pointer;
		}
		
		footer {
			text-align: center;
			font-style: italic;
		}
	}
	
	@layer code {
		pre {
			border: 1px solid #dedede;
			padding: 1em;
			background: #f7f7f7;
			font-family: "Courier 10 Pitch", Courier, monospace;
			overflow-x: auto;
			border-left: 0.4em solid cornflowerblue;
			tab-size: 4;
		}
		
		code:not(pre code), output:not(code:has(output) output) {
			background: #f7f7f7;
			border: 1px solid rgb(0 0 0 / 0.2);
			padding: 0.1rem 0.3rem;
			margin: 0.1rem 0;
			border-radius: 0.2rem;
			display: inline-block;
		}
	}

	@layer support {
		.no-support,
		.has-support {
			margin: 1em 0;
			padding: 1em;
			border: 1px solid #ccc;
		}

		.no-support {
			background-color: #ff00002b;
		}
		.no-support[data-level="warn"] {
			background-color: #ffff002b;
		}
		.has-support {
			background-color: #00ff002b;
		}
		.no-support, [data-show-when-no-support] {
			display: block !important;
		}
		.has-support, [data-show-when-has-support] {
			display: none !important;
		}
		:is(.has-support, .no-support) > :first-child {
			margin-top: 0;
		}
		:is(.has-support, .no-support) > :last-child {
			margin-bottom: 0;
		}
		
		@property --supports-at-property {
			syntax: "*";
			initial-value: ;
			inherits: true;
		}
		.no-support[data-support="at-property"], [data-no-support="at-property"] {
			--value-when-supported: var(--supports-at-property) none;
			--value-when-not-supported: block;
			display: var(--value-when-supported, var(--value-when-not-supported)) !important;
		}
		.has-support[data-support="at-property"], [data-has-support="at-property"] {
			--value-when-supported: var(--supports-at-property) block;
			--value-when-not-supported: none;
			display: var(--value-when-supported, var(--value-when-not-supported)) !important;
		}

		@supports (transform: scaleX(cos(360deg))) {
			.no-support[data-support="css-trig-fns"] {
				display: none !important;
			}
			.has-support[data-support="css-trig-fns"], [data-show-when-has-support="css-trig-fns"] {
				display: block !important;
			}
		}
	}
	
	@layer nth-child {
		[data-countchildren] > :nth-child(1) {
			--nth-child: 1;
		}
		[data-countchildren] > :nth-child(2) {
			--nth-child: 2;
		}
		[data-countchildren] > :nth-child(3) {
			--nth-child: 3;
		}
		[data-countchildren] > :nth-child(4) {
			--nth-child: 4;
		}
		[data-countchildren] > :nth-child(5) {
			--nth-child: 5;
		}
		[data-countchildren] > :nth-child(6) {
			--nth-child: 6;
		}
		[data-countchildren] > :nth-child(7) {
			--nth-child: 7;
		}
		[data-countchildren] > :nth-child(8) {
			--nth-child: 8;
		}
		[data-countchildren] > :nth-child(9) {
			--nth-child: 9;
		}
		[data-countchildren] > :nth-child(10) {
			--nth-child: 10;
		}

		[data-countchildren]:has(> :nth-child(1):last-child) > * {
			--nth-siblings: 0;
		}
		[data-countchildren]:has(> :nth-child(2):last-child) > * {
			--nth-siblings: 1;
		}
		[data-countchildren]:has(> :nth-child(3):last-child) > * {
			--nth-siblings: 2;
		}
		[data-countchildren]:has(> :nth-child(4):last-child) > * {
			--nth-siblings: 3;
		}
		[data-countchildren]:has(> :nth-child(5):last-child) > * {
			--nth-siblings: 4;
		}
		[data-countchildren]:has(> :nth-child(6):last-child) > * {
			--nth-siblings: 5;
		}
		[data-countchildren]:has(> :nth-child(7):last-child) > * {
			--nth-siblings: 6;
		}
		[data-countchildren]:has(> :nth-child(8):last-child) > * {
			--nth-siblings: 7;
		}
		[data-countchildren]:has(> :nth-child(9):last-child) > * {
			--nth-siblings: 8;
		}
		[data-countchildren]:has(> :nth-child(10):last-child) > * {
			--nth-siblings: 9;
		}
	}
}
!

JS 

              
                const $visual = document.querySelector('#visual');
const $add = document.querySelector('button[data-trigger="add"]');
const $remove = document.querySelector('button[data-trigger="remove"]');

let numDots = document.querySelectorAll('.dot').length;
const maxNumDots = 10;

$add.addEventListener('click', e => {
	if (numDots == maxNumDots) return;
	
	// Create new dot and append it
	const $newDot = document.createElement('span');
	$newDot.classList.add('dot');
	$visual.appendChild($newDot);
	
	numDots++;
});

$remove.addEventListener('click', e => {
	if (numDots == 1) return;
	
	// Find last dot and remove it
	const $lastDot = $visual.querySelector(':scope > .dot:last-child');
	$lastDot.remove();
	
	numDots--;
});

// Firefox does not support :has() yet, so we have to set the --nth-siblings count through JS
const supportsComplexHas = CSS.supports('selector(:has(>*))');
if (!supportsComplexHas) {
	const updateChildCount = ($parent) => {
		$parent.querySelectorAll(':scope > *').forEach($child => {
			$child.style.setProperty('--nth-siblings', $parent.childElementCount - 1);
		});
	};
	const updateChildCountAll = () => {
		document.querySelectorAll('[data-countchildren]').forEach($parent => {
			updateChildCount($parent);
		});
	}
	updateChildCountAll();
	
	$add.addEventListener('click', e => {
		updateChildCount($visual);
	});
	$remove.addEventListener('click', e => {
		updateChildCount($visual);
	});
}
!
999px

Console