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CSS

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CSS Base

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JavaScript

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HTML 

              
                <p><em>💡 With atan2, you can calculate the rotation for an object so that it points back to a specific point</em></p>

<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>

<div class="origin">
	<div class="box"></div>
	<div class="box"></div>
</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 

              
                .origin {
	position: relative;
	width: 600px;
	height: 400px;
	border: 1px solid #333;
	--mouse-x: 0;
	--mouse-y: 0;
	overflow: hidden;
	border-radius: 0.5em;
	touch-action: none;
}

.origin::before {
	content: '';
	height: 20px;
	width: 20px;
	translate: calc((var(--mouse-x) * 1px) - 50%) calc((var(--mouse-y) * 1px) - 50%);
	background: black;
	position: absolute;
	border-radius: 50%;
	pointer-events: none;
	z-index: -1;
}

div.box {
	--my-x: 50;
	--my-y: 300;

	width: 50px;
	height: 50px;

	background: linear-gradient(orange, red);
	border-top: 2px solid lime;
	transform-origin: 50% 50%;
	pointer-events: none;
	position: absolute;
	
	/* Position of the box inside its parent */
	translate: calc((var(--my-x) * 1px)) calc(var(--my-y) * 1px);
	
	/* Rotate so that the box faces the mouse position */
	/* For this, take the box’s own position and size (25 = half the width) into account */
	rotate: atan2(
		calc((var(--mouse-x) - var(--my-x) - 25) * 1),
		calc((var(--mouse-y) - var(--my-y) - 25) * -1)
	);
}

div.box:nth-child(2) {
	--my-x: 500;
	--my-y: 50;
}

div.box::before {
	content: '';
	display: block;
	width: 2px;
	height: 1000px;
	background: black;
	position: absolute;
	left: 50%;
	transform: translateX(-50%);
	bottom: 100%;
}


/* Non-demo styles below */
@layer base {
	@layer reset {
		* {
			box-sizing: border-box;
		}
		body {
			margin: 0;
			padding: 0;
		}
		html, body {
			min-height: 100%;
		}
	}
	@layer layout {
		html {
			max-width: 84ch;
			padding: 3rem 2rem;
			margin: auto;
		}
		body {
			display: grid;
			place-content: safe center;
			gap: 1em;
		}
		
		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;
		}
		
		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;
			display: block;
		}
		.no-support[data-level="warn"] {
			background-color: #ffff002b;
		}
		.has-support {
			background-color: #00ff002b;
			display: none;
		}
		:is(.has-support, .no-support) > :first-child {
			margin-top: 0;
		}
		:is(.has-support, .no-support) > :last-child {
			margin-bottom: 0;
		}

		@supports (transform: scaleX(cos(360deg))) {
			.no-support[data-support="css-trig-fns"] {
				display: none;
			}
			.has-support[data-support="css-trig-fns"] {
				display: block;
			}
		}
	}
}
!

JS 

              
                // Track mouse position over .origin
const $origin = document.querySelector(".origin");

$origin.addEventListener("pointermove", (evt) => {
  let x = evt.offsetX;
  let y = evt.offsetY;

  $origin.style.setProperty("--mouse-x", Math.round(x));
  $origin.style.setProperty("--mouse-y", Math.round(y));
});
!
999px

Console