Pen Settings

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

The resource you are linking to is using the 'http' protocol, which may not work when the browser is using https.

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.

Powered by Algolia
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.

Learn more

+ add another resource

JavaScript

About JavaScript Preprocessors

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

Learn more · Versions

Babel includes JSX processing.

Add External Scripts/Pens

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

Powered by Algolia
About External Resources

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.

If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

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

+ add another resource

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.

Powered by Algolia
About Packages

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.

All packages are different, so refer to their docs for how they work.

If you're using React / ReactDOM, make sure to turn on Babel for the JSX processing.

Behavior

Auto Save

If active, Pens will autosave every 30 seconds after being saved once.

Auto-Updating Preview

If enabled, the preview panel updates automatically as you code. If disabled, use the "Run" button to update.

Format on Save

If enabled, your code will be formatted when you actively save your Pen. Note: your code becomes un-folded during formatting.

Editor Settings

Code Indentation

Want to change your Syntax Highlighting theme, Fonts and more?

Visit your global Editor Settings.

HTML 

              
                - const BASE = 'https://developer.mozilla.org/en-US/docs/Web/HTML/Element/';
- const DATA = [ // tabs content data
- 	{
-			name: 'slider', 
- 		desc: 'Define a slider others can update.', 
- 		link: 'input/range'
- 	}, 
- 	{
-			name: 'number input', 
- 		desc: 'Create a number.', 
- 		link: 'input/number'
- 	}, 
- 	{
-			name: 'table', 
- 		desc: 'Create a table to input data.', 
- 		link: 'table'
- 	}
- ];
- const N = DATA.length; // number of tabs

- let k = 0; // selected tab index on page load
- let r = 5; // tab rounding

style
	- for(let i = 0; i < N; i++)
		- let j = i + 1;
		| /* tab and tab panel indices */
		| [role^=tab]:nth-of-type(#{j}) { --i: #{i} }
		| /* tab panel flag based on corresponding tab 
		|  * being hovered or focused */
		|	:has([role=tab]:nth-child(#{j}):is(:hover, :focus)) 
		| [role=tabpanel]::nth-of-type(#{j}) { --hov: 1 }

svg(width='0' height='0' aria-hidden='true')
	filter#roundstroke(color-interpolation-filters='sRGB')
		// extract just the semi-transparent tab "border-color"
		// and make it go from alpha = .5 to fully opaque
		feComponentTransfer
			feFuncA(type='table' tableValues='0 1 0')
		// dilate it to make it intersect tab shape edges
		feMorphology(operator='dilate' radius=2*r result='line')
		// extract just the fully opaque no rounding tab shape
		feComponentTransfer(in='SourceGraphic')
			feFuncA(type='table' tableValues='0 0 1')
		// blur has the side effect of rounding corners
		feGaussianBlur(stdDeviation=r result='blur')
		// also creates semitransparent edge pixels
		// push alpha of most (not all) towards either 0 or 1
		// whichever is closer, using out of bounds values
		// depending on the r value; save as 'fill'
		// this gives us the rounded tab
		feComponentTransfer(result='fill')
			feFuncA(type='table' 
			        tableValues=`${-1*Math.round(Math.sqrt(2*r))} ${r + 1}`)
		// now for the tab border
		// push alpha of most (not all) semitransparent pixels
		// towards either 0 or 1 as follows:
		// close to either 0 or 1 => push towards 0
		// close to .5 => push towards 1
		feComponentTransfer(in='blur')
			feFuncA(type='table' 
			        tableValues=[-r, r, -r].join(' '))
		// keep the "border-color" area only within this shape
		feComposite(in='line' operator='in')
		// place the no line rounded tab on top
		feBlend(in='fill')

main
	h1#title Tabs with rounded corners & borders
	section.tabs(style=`--n: ${N}; --k: ${k}; --r: ${r}px`)
		nav.tablist(role='tablist' aria-labelledby='title')
			- for(let i = 0; i < N; i++)
				- let c = DATA[i];
				button(role='tab' 
				       id=`tab${i}` aria-controls=`panel${i}` 
				       aria-selected=i ? 'false' : 'true' 
							 tabindex=i ? -1 : 0) #{c.name}
		- for(let i = 0; i < N; i++)
			- let c = DATA[i];
			div(role='tabpanel' 
			    id=`panel${i}` aria-labelledby=`tab${i}` 
			    aria-hidden=i ? 'true' : 'false')
				.back(aria-hidden='true')
				.content
					p #{c.desc} 
						a(href=`${BASE}${c.link}` target='_blank') Link
						| .
!

CSS 

              
                @import url('https://fonts.googleapis.com/css2?family=Kode+Mono:wght@400..700&family=Shantell+Sans:wght@300..800&display=swap');

/* grid 'em all  */
html, body, main, section, nav, div { display: grid }

html { min-height: 100% }

body {
	place-content: center;
	grid-template-columns: Min(100%, 40em);
	overflow-x: hidden; /* juust in case */
	/* image background to show there are no covers */
	background: 
		url(https://images.unsplash.com/photo-1534577403868-27b805ca4b9c?w=2400) 
			50%/ cover #191c1f;
	background-blend-mode: multiply;
	color: #ededed; /* contrasting text */
	font: 300 clamp(.75em, 6.25vw, 1.5em)/ 1.125 
		shantell sans, cursive
}

/* svg only to contain filter which alters graphic result
 * so it's functionally the same as a style element, 
 * take it out of document flow */
svg[aria-hidden='true'] { position: fixed }

h1 {
	font-weight: 500;
	text-align: center;
	text-wrap: balance
}

a, button, div { --hov: 0 }

a { color: limegreen }

:focus { outline: dotted 1px }

:is(a, button):is(:hover, :focus) { --hov: 1 }

.tabs {
	/* no gap between tab & corresponding tab panel (row)
	 * only between tabs (column gap) */
	grid-gap: 0 Max(.375em, calc(2*var(--r)));
	grid-template: 
		repeat(2, max-content)/ 
		Max(5%, 3*var(--r)) /* first tab offset */ 
		/* the n tabs, sized by their content */
		repeat(var(--n), max-content) 
		1fr /* space after last tab */;
	font-family: kode mono, monospace
}

[role='tablist'] {
	/* ensure it's on top of selected tab panel */
	z-index: 2;
	/* make it occupy the entire first row */
	grid-area: 1/ 1/ span 1/ -1;
	/* and inherit columns */
	grid-template-columns: subgrid
}

[role*='tab'] {
	/* difference between selected tab & this tab index */
	--dif: var(--k) - var(--i);
	/* NOT selected flag; 
	 * 0 if selected (ON), 1 if not selected (OFF) */
	--not: Min(1, Max(var(--dif), -1*(var(--dif))));
	/* is selected flag; 
	 * 1 if selected (ON), 0 if not selected (OFF) */
	--sel: calc(1 - var(--not));
	/* percentage value based on this flag
	 * 100% if selected, 0% if not */
	--prc: calc(var(--sel)*100%);
	color: /* based on is selected flag */
		color-mix(in srgb, 
			/* sel ON, hov irrelevant */
			#04e4a4 var(--prc), 
			/* sel OFF, based on is hovered flag */
			color-mix(in srgb, 
					#746c76 /* hov ON */ calc(var(--hov)*100%), 
					#3d4144 /* hov OFF */))
}

[role='tab'] {
	/* column depending on its index */
	grid-area: 1/ calc(var(--i) + 2);
	overflow: hidden; /* prevent spillout if needed */
	/* focus ring space in from border */
	outline-offset: calc(-2*var(--r));
	border: none; /* override browser default */
	padding: .5em .75em; /* give the text some space */
	/* limit its width */
	max-width: Max(3em, 100vw/(var(--n) + 1));
	background: none; /* override browser default */
	font: inherit; /* override browser default */
	font-weight: 700; /* make it stand out */
	/* some refining touches */
	text-overflow: ellipsis;
	text-transform: capitalize;
	white-space: nowrap;
	cursor: pointer
}

[role='tabpanel'] {
	/* make it occupy entire grid */
	grid-area: 1/ 1/ -1/ -1;
	/* and inherit both rows and columns */
	grid-template: subgrid/ subgrid;
	/* sepends on selection status */
	z-index: var(--sel)
}

.back {
	/* make it cover entire parent grid */
	grid-area: 1/ 1/ -1/ -1;
	/* and inherit entire parent grid, both rows & cols */
	grid-template: subgrid/ subgrid;
	/* cancel out padding */
	margin: calc(-1*var(--r));
	/* make some space around its pseudos 
	 * that create the basic no rounding tab shape */
	padding: var(--r);
	/* semitransparent outer area outside pseudos 
	 * this gets extrated to create the border  
	 * using its RGB channels */
	background: 
		color-mix(in srgb, currentcolor, #0000);
	/* this rounds the shape created by the pseudos
	 * and gives it a border */
	filter: url(#roundstroke);
	
	&::before, &::after {
		background: 
			/* depends on selection status */
			color-mix(in srgb, 
				#101214 var(--prc) /* when selected */, 
				#202428 /* when not selected */);
		content: ''
	}
	
	/* put it in same cell as corresponding tab (button) */
	&::before { grid-area: 1/ calc(var(--i) + 2) }
	
	/* make it cover entire second row (content area) */
	&::after { grid-area: 2/ 1/ -1/ -1 }
}

.content {
	/* make it occupy second row */
	grid-area: 2/ 1/ span 1/ -1;
	align-content: start;
	/* this text content on top of its back sibling 
	 * responsible for background and border */
	z-index: 1;
	padding: .5em;
	min-height: 9em;
	color: #dedede;
	
	[role='tabpanel'][aria-hidden='true'] & {
		display: none
	}
}
!

JS 

              
                const _TABS = document.querySelector('.tabs'), 
			_LIST = [..._TABS.querySelectorAll('button[role=tab]')], 
			_PANE = [..._TABS.querySelectorAll('[role=tabpanel]')], 
			N = _LIST.length;

let k = _TABS.style.getPropertyValue('--k');

function switchAttr(e1, e2, attr) {
	[e1[attr], e2[attr]] = [e2[attr], e1[attr]]
}

function switchTabs(i) {
	switchAttr(_LIST[i], _LIST[k], 'ariaSelected');
	switchAttr(_PANE[i], _PANE[k], 'ariaHidden');
	
	/* for some reason, switching like above doesn't work */
	_LIST[i].tabIndex = 0;
	_LIST[k].tabIndex = -1;
	
	_LIST[i].focus();
	_TABS.style.setProperty('--k', k = i)
}

addEventListener('click', e => {
	let _t = e.target, i = _LIST.indexOf(_t);
	
	if(i > -1) switchTabs(i)
});

addEventListener('keyup', e => {
	let _t = e.target, i = _LIST.indexOf(_t);
	
	if(i !== -1) {
		console.log(e.keyCode)
		switch(e.keyCode) {
			case 39: // ->
				switchTabs((k + 1)%N);
				break;
			case 37: // <-
				switchTabs((k + N - 1)%N);
				break;
			case 36: // HOME
				switchTabs(0);
				break;
			case 35: // END
				switchTabs(N - 1);
				break;
		}
	}
});
!
999px

Console