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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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Babel includes JSX processing.

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HTML 

              
                <div class="support">
	<p>This demo uses anchor positioning which is not widely supported outside of Chromium based browsers. <a href="https://caniuse.com/?search=anchor-">Check out browser compatability here</a></p>
</div>

<div class="mouse-cursor"></div>
<div class="mouse-click-point"></div>
<div class="rectangle"></div>
!

CSS 

              
                body {
	/* 	This bit is the mouse cursor. From another demo of mine, but using it here too to give a couple of circles where the mouse cursor is. Getting the position of the mouse from mousemove event in JS and two custom properties */
	background-image: radial-gradient(
			16px at calc(var(--mouse-x) * 100vw) calc(var(--mouse-y) * 100vh),
			rgba(0, 0, 0, 0) 17px,
			rgba(0, 0, 0, 1) 18px,
			rgba(0, 0, 0, 0) 19px
		),
		radial-gradient(
			16px at calc(var(--mouse-x) * 100vw) calc(var(--mouse-y) * 100vh),
			rgba(0, 0, 0, 0) 11px,
			rgba(0, 0, 0, 1) 12px,
			rgba(0, 0, 0, 0) 13px
		);
	/* end of mouse cursor */

	height: 100vh;
	width: 100vw;
	container-type: size;

	position: relative;
}

/* This is where the current mouse position is. Needed to be able to draw the rectangle from the current mouse position to where the user clicked last */
.mouse-cursor {
	--background: rgb(from purple r g b / 0.75);
	--is: --start;
	--dimension: 15px;

	border-radius: 50%;

	translate: 0% 0%;

	left: max(
		calc(var(--_dimension) / -2),
		calc(calc(var(--mouse-x, 0) * 100cqi) - calc(var(--_dimension) / 2))
	);
	top: max(
		calc(var(--_dimension) / -2),
		calc(calc(var(--mouse-y, 0) * 100cqb) - calc(var(--_dimension) / 2))
	);
}

.mouse-click-point {
	--background: blue;
	--is: --end;

	top: calc(var(--mouse-click-y, 0.5) * 100cqb);
	left: calc(calc(var(--mouse-click-x, 0.5) * 100cqi));
}

[class^="mouse"] {
	position: absolute;
	--_dimension: var(--dimension, 30px);
	aspect-ratio: 1;
	height: var(--_dimension);
	anchor-name: var(--is);
	background-color: var(--background);
}

.rectangle {
	/* 	Adding onto the idea by Kizu here: https://kizu.dev/anchor-positioning-experiments/ */
	--_from: var(--from, --start);
	--_to: var(--to, --end);

	top: min(anchor(var(--_from) center), anchor(var(--_to) center));
	left: min(anchor(var(--_from) center), anchor(var(--_to) center));
	right: min(anchor(var(--_from) center), anchor(var(--_to) center));
	bottom: min(anchor(var(--_from) center), anchor(var(--_to) center));

	background: oklab(from hotpink l a calc(b * 3) / 1.75);

	position: absolute;

	/* Technique found here: https://css-irl.info/css-halftone-patterns/	 */
	--dotSize: 0.15rem;
	--bgSize: 0.5rem;
	--bgPosition: calc(var(--bgSize) / 2);

	background: radial-gradient(red, hotpink);

	mask-image: radial-gradient(
			circle at center,
			black var(--dotSize),
			transparent 0
		),
		radial-gradient(circle at center, black var(--dotSize), transparent 0);
	mask-size: var(--bgSize) var(--bgSize);
	mask-position: 0 0, var(--bgPosition) var(--bgPosition);
}

.support {
	max-inline-size: 90%;
	margin-inline: auto;
	margin-top: 2.5cqi;

	border: 3px double red;
	padding: 3rem;

	@supports (anchor-name: --foo) {
		display: none;
	}
}
!

JS 

              
                const root = document.documentElement;

const setVariables = (evt, name) => {
	let x = evt.clientX / innerWidth;
	let y = evt.clientY / innerHeight;

	root.style.setProperty(`--${name}-x`, x);
	root.style.setProperty(`--${name}-y`, y);
};

document.addEventListener("mousemove", (evt) => {
	setVariables(evt, "mouse");
});

document.addEventListener("click", (evt) => {
	setVariables(evt, "mouse-click");
});
!
999px

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