existenzial/base.css

## base.css
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  height: 100vh;
  width: 100vw;
  background: whitesmoke;
}

.color-box {
  display: flex;
  justify-content: center;
  align-items: center;
  height: 300px;
  width: 300px;
  cursor: pointer;
  background: #fff;
  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1),
    0 2px 4px -1px rgba(0, 0, 0, 0.06);
  transition: all 0.2s ease-out;
}

.color-box:hover {
  box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1),
    0 10px 10px -5px rgba(0, 0, 0, 0.04);
}

.nested-box {
  height: 75px;
  width: 75px;
  transition: all 0.2s ease-out;
  background: blueviolet;
}

.title {
  color: #ccc;
  font-size: 2.5em;
  margin: 100px;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  letter-spacing: 0.25em;
}

## index.html
<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <meta http-equiv="X-UA-Compatible" content="ie=edge" />
    <link rel="stylesheet" href="styles/base.css" />
    <link rel="stylesheet" href="styles/main.css" />
    <title>CSS Variables</title>
  </head>

  <body>
    <h1 class="title"></h1>
    <div class="color-box">
      <div class="nested-box"></div>
    </div>

    <script src="js/main.js"></script>
  </body>
</html>

## main.css
/*
*
*
*
********************************
* Feature Query / Check Support
********************************
*/

@supports (--css: variables) {
  .color-box:hover .nested-box {
    background: turquoise;
  }
}

/*
*
*
*
********************************
* Global Variables
********************************
*/

/* attach to :root pseudo-class */
:root {
  --my-new-height: 25px;
}

.color-box:hover .nested-box {
  height: var(--my-new-height);
}

/*
*
*
*
********************************
* Local Variables
********************************
*/

/* attach to element */
.color-box {
  --bigger: scale(1.2);
}

.color-box:hover {
  transform: var(--bigger);
}

/*
*
*
*
********************************
* Internationalization
********************************
*/

/* use to for language-dependent values */
:root,
:root:lang(en) {
  --title: 'Box';
}

:root:lang(es) {
  --title: 'Caja';
}

:root:lang(fr) {
  --title: 'Boîte';
}

:root:lang(ar) {
  --title: 'صندوق';
}

.title::after {
  content: var(--title);
}

/*
*
*
*
********************************
* Calculated Values
********************************
*/

/* use for dynamically computed values */
.color-box {
  --x-pos: 0;
  --y-pos: 0;

  transform: translate(var(--x-pos), var(--y-pos));
}

## main.js
const colorBox = document.querySelector('.color-box');

// GET PROPERTIES
colorBox.style.getPropertyValue('--x-pos');
colorBox.style.getPropertyValue('--y-pos');

// using global getComputedStyle
getComputedStyle(colorBox).getPropertyValue('--x-pos');
getComputedStyle(colorBox).getPropertyValue('--y-pos');

console.group('Before');
console.log({
  x: colorBox.style.getPropertyValue('--x-pos'),
  y: colorBox.style.getPropertyValue('--y-pos'),
});
console.groupEnd();

// SET PROPERTIES
colorBox.style.setProperty('--x-pos', '100px');
colorBox.style.setProperty('--y-pos', '-75px');


console.group('After');
console.log({
  x: colorBox.style.getPropertyValue('--x-pos'),
  y: colorBox.style.getPropertyValue('--y-pos'),
});
console.groupEnd();
	* {
	margin: 0;
	padding: 0;
	box-sizing: border-box;
	}

	body {
	display: flex;
	justify-content: center;
	align-items: center;
	flex-direction: column;
	height: 100vh;
	width: 100vw;
	background: whitesmoke;
	}

	.color-box {
	display: flex;
	justify-content: center;
	align-items: center;
	height: 300px;
	width: 300px;
	cursor: pointer;
	background: #fff;
	box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1),
	0 2px 4px -1px rgba(0, 0, 0, 0.06);
	transition: all 0.2s ease-out;
	}

	.color-box:hover {
	box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1),
	0 10px 10px -5px rgba(0, 0, 0, 0.04);
	}

	.nested-box {
	height: 75px;
	width: 75px;
	transition: all 0.2s ease-out;
	background: blueviolet;
	}

	.title {
	color: #ccc;
	font-size: 2.5em;
	margin: 100px;
	font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
	letter-spacing: 0.25em;
	}
	<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8" />
	<meta name="viewport" content="width=device-width, initial-scale=1.0" />
	<meta http-equiv="X-UA-Compatible" content="ie=edge" />
	<link rel="stylesheet" href="styles/base.css" />
	<link rel="stylesheet" href="styles/main.css" />
	<title>CSS Variables</title>
	</head>

	<body>
	<h1 class="title"></h1>
	<div class="color-box">
	<div class="nested-box"></div>
	</div>

	<script src="js/main.js"></script>
	</body>
	</html>
	/*
	*
	*
	*
	********************************
	* Feature Query / Check Support
	********************************
	*/

	@supports (--css: variables) {
	.color-box:hover .nested-box {
	background: turquoise;
	}
	}

	/*
	*
	*
	*
	********************************
	* Global Variables
	********************************
	*/

	/* attach to :root pseudo-class */
	:root {
	--my-new-height: 25px;
	}

	.color-box:hover .nested-box {
	height: var(--my-new-height);
	}

	/*
	*
	*
	*
	********************************
	* Local Variables
	********************************
	*/

	/* attach to element */
	.color-box {
	--bigger: scale(1.2);
	}

	.color-box:hover {
	transform: var(--bigger);
	}

	/*
	*
	*
	*
	********************************
	* Internationalization
	********************************
	*/

	/* use to for language-dependent values */
	:root,
	:root:lang(en) {
	--title: 'Box';
	}

	:root:lang(es) {
	--title: 'Caja';
	}

	:root:lang(fr) {
	--title: 'Boîte';
	}

	:root:lang(ar) {
	--title: 'صندوق';
	}

	.title::after {
	content: var(--title);
	}

	/*
	*
	*
	*
	********************************
	* Calculated Values
	********************************
	*/

	/* use for dynamically computed values */
	.color-box {
	--x-pos: 0;
	--y-pos: 0;

	transform: translate(var(--x-pos), var(--y-pos));
	}
	const colorBox = document.querySelector('.color-box');

	// GET PROPERTIES
	colorBox.style.getPropertyValue('--x-pos');
	colorBox.style.getPropertyValue('--y-pos');

	// using global getComputedStyle
	getComputedStyle(colorBox).getPropertyValue('--x-pos');
	getComputedStyle(colorBox).getPropertyValue('--y-pos');

	console.group('Before');
	console.log({
	x: colorBox.style.getPropertyValue('--x-pos'),
	y: colorBox.style.getPropertyValue('--y-pos'),
	});
	console.groupEnd();

	// SET PROPERTIES
	colorBox.style.setProperty('--x-pos', '100px');
	colorBox.style.setProperty('--y-pos', '-75px');


	console.group('After');
	console.log({
	x: colorBox.style.getPropertyValue('--x-pos'),
	y: colorBox.style.getPropertyValue('--y-pos'),
	});
	console.groupEnd();