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HTML

About HTML Preprocessors

HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

Learn more · Versions

Adding Classes

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

!
Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

Learn more · Versions

CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

Add External Stylesheets/Pens

Any URLs added here will be added as <link>s in order, and before the CSS in the editor. You can use the CSS from another Pen by using its URL and the proper URL extension.

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About External Resources

You can apply CSS to your Pen from any stylesheet on the web. Just put a URL to it here and we'll apply it, in the order you have them, before the CSS in the Pen itself.

You can also link to another Pen here (use the .css URL Extension) and we'll pull the CSS from that Pen and include it. If it's using a matching preprocessor, use the appropriate URL Extension and we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

Learn more · Versions

Babel includes JSX processing.

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You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

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You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

Learn more

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Packages

Add Packages

Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

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HTML 

              
                <details>
  <summary>
    <span data-css-icon="down">Down To Up<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus">Plus To Minus<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right">Right To Down<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross">Plus to Cross<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals">Equals to Cross<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="down outline">Down To Up: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus outline">Plus To Minus: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right outline">Right To Down: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross outline">Plus to Cross: Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals outline">Equals to Cross: Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="down fill">Down To Up: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus fill">Plus To Minus: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right fill">Right To Down: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross fill">Plus to Cross: Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals fill">Equals to Cross: Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square down outline">Down To Up: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square plus outline">Plus To Minus: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square right outline">Right To Down: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square cross outline">Plus to Cross: Square Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square equals outline">Equals to Cross: Square Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square down fill">Down To Up: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square plus fill">Plus To Minus: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square right fill">Right To Down: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square cross fill">Plus to Cross: Square Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square equals fill">Equals to Cross: Square Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae</div>
</details>

<h2>Menu: Requires extra element for outline/fill</h2>
<details>
  <summary>
    <span data-css-icon="menu">Menu to Cross<i></i></span>
  </summary>
 <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<div dir="rtl">
  <h2> right-to-left</h2>
 <details>
  <summary>
    <span data-css-icon="down">Down To Up<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus">Plus To Minus<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right">Right To Down<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross">Plus to Cross<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals">Equals to Cross<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="down outline">Down To Up: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus outline">Plus To Minus: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right outline">Right To Down: Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross outline">Plus to Cross: Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals outline">Equals to Cross: Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="down fill">Down To Up: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="plus fill">Plus To Minus: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="right fill">Right To Down: Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="cross fill">Plus to Cross: Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="equals fill">Equals to Cross: Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square down outline">Down To Up: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square plus outline">Plus To Minus: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square right outline">Right To Down: Square Outline<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square cross outline">Plus to Cross: Square Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square equals outline">Equals to Cross: Square Outline<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square down fill">Down To Up: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit, amet consectetur adipisicing elit. Eos minus quo ipsam culpa! Dicta, reiciendis.
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square plus fill">Plus To Minus: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsam commodi amet fuga dicta facilis! Sed ipsum unde cumque debitis omnis placeat non, ut magni dolores!
  </div>
</details>

<details>
  <summary>
    <span data-css-icon="square right fill">Right To Down: Square Fill<i></i></span>
  </summary>
  <div>Lorem ipsum dolor, sit amet consectetur adipisicing elit. Odit, quam. Ipsum deserunt veniam placeat iusto vel possimus omnis quo dolor distinctio fugit. Ex, impedit est?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square cross fill">Plus to Cross: Square Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>

<details>
  <summary>
    <span data-css-icon="square equals fill">Equals to Cross: Square Fill<i></i></span>
  </summary>
  <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae</div>
</details>

<h2>Menu: Requires extra element for outline/fill</h2>
<details>
  <summary>
    <span data-css-icon="menu">Menu to Cross<i></i></span>
  </summary>
 <div>Lorem, ipsum dolor sit amet consectetur adipisicing elit. Numquam ab animi velit est unde, quod, debitis voluptas, tenetur possimus corporis veritatis commodi eveniet placeat officiis non! Et consequatur nulla molestiae?</div>
</details>
</div>
!

CSS 

              
                /*
For further documentation about CSS Icons, see this pen:
https://codepen.io/stoumann/pen/eYzPVqe
*/

[data-css-icon] {
	--animdur: .3s;
  --loading-animdur: 0.8s;
	--animtf: ease-in;
	--bdw: 2px;
  --bdrs: 50%;
  --bgc: transparent;
	--c: currentcolor;
  --dots-bgc: silver;
  --dots-size: 0.5rem;
  --icon-size: 1rem;
	--size: 2.5rem;

	align-items: center;
  cursor: pointer;
	display: flex;
	justify-content: space-between;
}
[data-css-icon] i {
  align-items: center;
  background-color: var(--bgc);
  border-radius: var(--bdrs);
  box-sizing: border-box;
  display: inline-flex;
  height: var(--size);
  justify-content: center;
  position: relative;
  transition: background-color var(--animdur) var(--animtf);
  width: var(--size);
}
[data-css-icon] i::after,
[data-css-icon] i::before {
  transform-origin: 50% 50%;
	transition: all var(--animdur) var(--animtf);
}

[data-css-icon*="down"] i::after,
[data-css-icon*="right"] i::after {
  background: transparent;
	border-color: var(--c);
	border-style: solid;
  box-sizing: border-box;
	content: '';
	display: inline-block;
	height: var(--icon-size) ;
	margin: 0;
  position: relative;
	width: var(--icon-size);
}
[data-css-icon*="down"] i::after {
	border-width: 0 var(--bdw) var(--bdw) 0;
  top: calc(0px - (var(--icon-size) / 4));
  transform: rotate(45deg);
}
[data-css-icon*="right"] i::after {
	border-width: var(--bdw) var(--bdw) 0 0;
  right: calc((var(--icon-size) / 4));
  top: 0;
	transform: rotate(45deg);
}

[data-css-icon*="equals"] i::after,
[data-css-icon*="equals"] i::before,
[data-css-icon*="cross"] i::after,
[data-css-icon*="cross"] i::before,
[data-css-icon*="menu"] i,
[data-css-icon*="menu"] i::after,
[data-css-icon*="menu"] i::before,
[data-css-icon*="plus"] i::after,
[data-css-icon*="plus"] i::before {
  /* Width need to be the diagonal of the down-arrow side-length (--size): sqrt(2) * --size. */
	--w: calc(var(--icon-size) * 1.4142135623730950488016887242097);
	background: var(--c);
	content: '';
	height: var(--bdw);
	position: absolute;
	width: var(--w);
}
[data-css-icon*="cross"] i::before,
[data-css-icon*="plus"] i::before {
	transform: rotate(90deg);
}
[data-css-icon*="equals"] i {
  --m: 4px;
}
[data-css-icon*="equals"] i::after {
  transform: translateY(var(--m));
}
[data-css-icon*="equals"] i::before {
  transform: translateY(calc(0px - var(--m)));
}
[data-css-icon*="dots"],
[data-css-icon*="menu"] {
  height: var(--size);
}
[data-css-icon*="menu"] i {
  --bdrs: 0;
  --m: 7px;
  position: relative;
  right: calc((var(--size) - var(--w)) / 2);
}
[data-css-icon*="menu"] i::after {
  top: var(--m);
}
[data-css-icon*="menu"] i::before {
  top: calc(0px - var(--m));
}

[data-css-icon*="dots"] i,
[data-css-icon*="dots"] i::after,
[data-css-icon*="dots"] i::before {
  animation: dots var(--loading-animdur) infinite alternate;
  background-color: var(--c);
  border-radius: 50%;
  content: "";
  display: inline-block;
  height: var(--dots-size);
  width: var(--dots-size);
}
[data-css-icon*="dots"] i {
  animation-delay: var(--loading-animdur);
  position: relative;
  right: calc((var(--size) - var(--dots-size)) / 4);
}
[data-css-icon*="dots"] i::after {
  animation-delay: 0s;
  left: calc(0px - (var(--dots-size) * 3));
  position: absolute;
}
[data-css-icon*="dots"] i::before {
  animation-delay: calc(var(--loading-animdur) / 2);
  left: calc(0px - (var(--dots-size) * 1.5));
  position: absolute;
}

[data-css-icon*="spin"] i::after {
  animation: spin var(--loading-animdur) infinite linear;
  border-radius: 50%;
  border: var(--bdw) solid var(--dots-bgc);
  border-left: var(--bdw) solid var(--c);
  content: "";
  height: var(--icon-size);
  transform: translateZ(0);
  width: var(--icon-size);
}

/* STATE */
[open] > summary > [data-css-icon*="cross"] i::after {
	transform: rotate(45deg);
}
[open] > summary > [data-css-icon*="cross"] i::before {
  transform: rotate(135deg);
}
[open] > summary > [data-css-icon*="down"] i::after {
  top: var(--bdw);
	transform: rotate(45deg) scale(-1) ;
}
[open] > summary > [data-css-icon*="right"] i::after {
  right: 0;
  top: calc(0px - (var(--icon-size) / 4));
	transform: rotate(135deg);
}
[open] > summary > [data-css-icon*="plus"] i::after {
	transform: rotate(180deg);
}
[open] > summary > [data-css-icon*="plus"] i::before {
	transform: rotate(-0deg);
}

[open] > summary > [data-css-icon*="equals"] i::after { transform: rotate(-45deg); }
[open] > summary > [data-css-icon*="equals"] i::before { transform: rotate(45deg); }

[open] > summary > [data-css-icon*="menu"] i { background-color: transparent; }
[open] > summary > [data-css-icon*="menu"] i::after { transform: translateY(calc(0px - var(--m))) rotate(-45deg); }
[open] > summary > [data-css-icon*="menu"] i::before { transform: translateY(var(--m)) rotate(45deg); }

/* RTL: inset-block-end fails */
[dir="rtl"] [data-css-icon*="right"] i::after {
	left: calc((var(--icon-size) / 4));
}
[dir="rtl"] [data-css-icon*="menu"] i {
	left: 0.5rem;
  right: auto;
}

/* MODIFIERS */
[data-css-icon*="outline"] i {
  border: var(--bdw) solid var(--c);
}
[data-css-icon*="fill"] {
  --bgc: hsl(195, 10%, 30%);
  --c: hsl(195, 10%, 95%);
}
[data-css-icon*="square"] {
  --bdrs: 5px;
}

/* For this demo only */
body { font-family: system-ui, sans-serif; padding: 1rem; }
button, details { width: 25rem; }
button { font-family: inherit; font-size: inherit; }
details {
  height: var(--collapsed);
  overflow: hidden;
  transition: height 300ms cubic-bezier(0.4, 0.01, 0.165, 0.99);
}
details[open] {
  height: var(--expanded);
}
button,
summary { 
  background-color: var(--bgc);
  border: 0;
  border-radius: 5px;
  color: var(--c, inherit);
  list-style-type: none;
  margin: 0.5rem 0;
  outline: none;
  padding-bottom: 0.5rem;
  padding-top: 0.5rem;
  padding-inline-end: 0.5rem;
  padding-inline-start: 1rem;
  user-select: none;
}
summary::marker { display: none; }
summary::-webkit-details-marker { display: none; }

/* 4 States of summary */
button,
summary {
  --bgc: hsl(195, 10%, 90%);
}
[open] > summary {
  --bgc: hsl(195, 10%, 20%);
  --c: hsl(195, 10%, 92%);
}
button:focus,
summary:focus {
  --bgc: hsl(195, 10%, 75%);
}
[open] > summary:focus {
  --bgc: hsl(195, 10%, 10%);
    --c: hsl(195, 10%, 99%);
}
[open] > summary:focus > [data-css-icon*="fill"],
[open] > summary > [data-css-icon*="fill"] {
  --bgc: hsl(195, 10%, 80%);
  --c: hsl(195, 10%, 10%);
}
summary + * {
  color: #777;
  line-height: 1.6;
  padding: 0.5rem;
}

@keyframes dots {
  0% {
    background-color: var(--c);
  }
  50%,
  100% {
    background-color: var(--dots-bgc);
  }
}

@keyframes spin {
  0% {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(1turn);
  }
}
!

JS 

              
                function setDetailsHeight(selector, wrapper = document) {
	const setHeight = (detail, open = false) => {
		detail.open = open;
		const rect = detail.getBoundingClientRect();
		detail.dataset.width = rect.width;
		detail.style.setProperty(open ? `--expanded` : `--collapsed`,`${rect.height}px`);
	}
	const details = wrapper.querySelectorAll(selector);
	const RO = new ResizeObserver(entries => {
		return entries.forEach(entry => {
			const detail = entry.target;
			const width = parseInt(detail.dataset.width, 10);
			if (width !== entry.contentRect.width) {
				detail.removeAttribute('style');
				setHeight(detail);
				setHeight(detail, true);
				detail.open = false;
			}
		})
	});
	details.forEach(detail => {
		RO.observe(detail);
	});
}

/* Run it */
setDetailsHeight('details');
!
999px

Console