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HTML

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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.

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Adding Classes

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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.

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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.

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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

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JavaScript

About JavaScript Preprocessors

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

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Babel includes JSX processing.

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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 

              
                <custom-button>Button Text</custom-button>
!

CSS 

              
                custom-button {
  border: 2px dotted red;
  padding: 1em 2em;
}
!

JS 

              
                const template = document.createElement("template");
template.innerHTML = /*html*/`
  <button><slot></slot></button>
`;

const sheet = new CSSStyleSheet();
sheet.replaceSync(/*css*/`
/* Defaults */
:host {
	display: contents;
	/* Style the "button" here, especially in ways that a consumer could _override_. */
  /* For instance... */
	border-radius: calc(Infinity * 1px);
	align-items: center;
	line-height: 1.5;
	border: 2px solid;
	font-weight: 500;
	cursor: pointer;
	width: max-content;
  padding: 5px 10px;
}
/* Pass all styles from :host to button */
button {
  all: inherit;
  display: inline-flex;
  box-sizing: border-box;
}
@media (prefers-reduced-motion: no-preference) {
	/* Because accessibility means so much more than just Tab keys and screen readers! */
	:host {
		transition:
			outline 0.3s ease-in-out,
			outline-offset 0.3s ease-in-out;
	}
}
/* Required */
/*
 * All of our elements need _something_ to be a specific way, like accessibility.
 * This prevents the consumer from futzing with those things.
 **/
button:not(:focus-visible) {
	outline: 2px solid transparent;
	outline-offset: 0px;
}
button:focus-visible {
	outline: 2px solid royalblue;
	outline-offset: 2px;
}
/* Overrides */
:host([disabled]) {
	background: var(--background-tertiary);
	color: var(--content-disabled);
	pointer-events: none;
}
`);

class CustomButton extends HTMLElement {
  constructor() {
    super();
    this.attachShadow({ mode: "open" });
    this.shadowRoot.appendChild(template.content.cloneNode(true));
    this.shadowRoot.adoptedStyleSheets = [sheet];
  }
}

customElements.define("custom-button", CustomButton);
!
999px

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