Pen Settings

HTML

CSS

CSS Base

Vendor Prefixing

Add External Stylesheets/Pens

Any URL's added here will be added as <link>s in order, and before the CSS in the editor. If you link to another Pen, it will include the CSS from that Pen. If the preprocessor matches, it will attempt to combine them before processing.

+ add another resource

JavaScript

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.

+ 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.

Behavior

Save Automatically?

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

              
                <h1>Accordion with <code>&lt;details&gt;</code> element</h1>
<p>Making the native <abbr>HTML</abbr> <code>&lt;details&gt;</code> element behave like a typical collapsible accordion with smooth animations.</p>

<p><input type="checkbox" id="accordion-toggle"><label for="accordion-toggle">Keep animations but remove auto-collapse effect </label></p>

<div class="container collapse">
  <details>
    <summary>Accordion heading 1</summary>
    <div class="details-wrapper">
      <div class="details-styling">        
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
      </div>
    </div>
  </details>
  <details>
    <summary>Accordion heading 2</summary>
    <div class="details-wrapper">
      <div class="details-styling">        
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
      </div>
    </div>
  </details>
  <details>
    <summary>Accordion heading 3</summary>
    <div class="details-wrapper">   
      <div class="details-styling">        
        <p>Lorem ipsum dolor sit amet consectetur adipisicing elit. Ipsa quis fuga saepe sunt delectus, quo assumenda dolorum officiis odit optio modi, aspernatur necessitatibus libero, itaque repellendus. Incidunt blanditiis magni velit.</p>
      </div>
    </div>
  </details>
</div>

<p>Using the <a href="https://github.com/javan/details-element-polyfill">details-element-polyfill</a> for IE/Edge support</p>
              
            
!

CSS

              
                // Classes set via JS
$accordionClass: '.collapse-init';
$panelClass: '.panel-active';
$contentsClass: 'summary + *';

/*
  Please wrap your collapsible content in a single element or so help me
  Must add a transition or it breaks because that's the whole purpose of this
  Only one transition-duration works (see explanation on line #141 in JS)
  You can add more to an inner wrapper (.details-styling)
*/
//Simplified: .details-wrapper{}
#{$accordionClass $contentsClass} {
  transition: all 0.25s ease-in-out;
  overflow: hidden; // because we're animating height
}

/*
  Closed state. Any CSS transitions work here
  The JS has a height calculation to make sliding opened/closed easier, but it's not necessary
  Remove the height prop for a simple toggle on/off (after all that work I did for you?)
*/
//Simplified: :not(.panel-active) .details-wrapper {}
#{$accordionClass} :not(#{$panelClass}) #{$contentsClass} {  
  height: 0;
  opacity: 0;
  transform: scale(0.9);
  transform-origin: bottom center;
}

// Let's get rid of the default arrows so we can style our own, as we must find whatever little joy we can in this garbage web
#{$accordionClass} {
  summary { list-style: none; } // Spec
  summary::-webkit-details-marker { display: none; } // Chrome
  summary::before { display: none; } // Polyfill
    
  // Should we do this? No idea
  summary { cursor: pointer; }
}

/*
  This element exists so .details-wrapper has no extra margin/padding that can screw with the smooth height collapse
  You can style .details-wrapper decoratively but avoid anything that modifies the box and add it to .details-styling instead
  Otherwise, this element is totally optional. Remove if you hate divitis
*/
.details-styling {
  padding: 1em;
}

//======= Non-essential page styling, ignore
$hue: 260;

$background: hsl($hue, 90, 98);
$text: hsl($hue, 20, 25);

$primary: hsl($hue, 85, 50);
$link: hsl($hue, 75, 65);
$border: hsl($hue, 20, 85);

::selection {
  $rot: 140;
  
  background: hsl($hue + $rot, 95, 70);
  color: adjust-hue($text, $rot);
}

html {
  background: $background;
  color: $text;
}

body {
  font: 1em/1.4 'Quicksand', sans-serif;
  margin: 0 auto;
  max-width: 960px;
  padding: 5vw;
}

h1 {
  font-size: 2em;
  margin-bottom: 1em;
  text-align: center;
  
  + p {
    margin-left: auto;
    margin-right: auto;
    max-width: 50ch;
  }
  
  ~ p {
    font-size: 1.2em;
    text-align: center;
  }
}

p {
  margin-top: 0;
  margin-bottom: 1em;
  
  &:last-child { margin-bottom: 0; }
}

code {
  $rot: 90;
  
  background: hsla($hue + $rot, 70, 70, 0.1);
  color: hsl($hue + $rot - 5, 75, 65);
}

a {
  color: $link;
  box-shadow: inset 0 -3px lighten($link, 20);
  font-weight: 700;
  text-decoration: none;
  transition: 0.2s;
  
  &:hover,
  &:focus {
    box-shadow: inset 0 -1.2em $link;
    color: $background;
  }
}

abbr {
  font-variant: small-caps;
  text-transform: lowercase;
  font-size: 1.2em;
}

[type=checkbox] {
  opacity: 0;
  position: absolute;
  width: 0;
  height: 0;
  
  + label {
    background: lighten($primary, 45);
    border-left: 4px solid $primary;
    cursor: pointer;
    display: block;
    font-size: 1rem;
    font-weight: 700;
    text-align: left;
    transition: 0.1s;
    padding: 0.75em 1em;
    
    &::before {
      border: 2px solid;
      border-radius: 2px;
      color: $primary;
      content: '';
      display: inline-block;
      margin-right: 0.75ch;
      transition: 0.1s;
      width: 1ch;
      height: 1ch;
      vertical-align: baseline;
    }
  }
  
  &:focus + label {
    outline: 2px solid $primary;    
  }
  
  &:checked + label::before {
    background: currentColor;
    box-shadow: inset 0 0 0 2px #fff;
  }
}

.container {
  box-shadow: 0.2em 1em 2em -1em $border;
  margin: 2.4em 0;
}

//==== Accordion element styling
details {
  $b: 6px;
  
  background: #fff;
  border: 1px solid $border;
  border-bottom: 0;
  list-style: none;
  
  &:first-child {
    border-radius: $b $b 0 0;
  }
  
  &:last-child {
    border-bottom: 1px solid $border;
    border-radius: 0 0 $b $b;
  }
}

summary {
  $arrow-size: 0.5em;
  
  display: block;
  transition: 0.2s;
  font-weight: 700;
  padding: 1em;
    
  &:focus {
    outline: 2px solid $primary;
  }
  
  #{$accordionClass} &::after {
    border-right: 2px solid;
    border-bottom: 2px solid;
    content: '';
    float: right;
    width: $arrow-size;
    height: $arrow-size;
    margin-top: $arrow-size/2;
    transform: rotate(45deg);
    transition: inherit;
  }
  
  [open] & {
    background: $primary;
    color: $background;
    
    &::after { 
      margin-top: $arrow-size;
      transform: rotate(225deg);
    }
  }
}
              
            
!

JS

              
                miscPolyfillsForIE();

/*
let accordion = new Collapse(element, { option: value}).init();

  Options - { option: defaultValue }
    accordion: false,
    initClass: 'collapse-init',
    activeClass: 'panel-active',
    heightClass: 'collapse-reading-height',

  Methods - accordion.method(panel)
    open(panel)
    close(panel)
    toggle(panel)
    openSinglePanel(panel) [AKA accordion mode]
    openAll()
    closeAll()

  Events - panel.addEventListener('event')
    openingPanel
    openedPanel
    closingPanel
    closedPanel
*/

class Collapse {
  constructor(container, options = {}) {
    let defaults = {
      accordion: false,
      initClass: 'collapse-init',
      activeClass: 'panel-active',
      heightClass: 'collapse-reading-height',
    }
    
    this.settings = Object.assign({}, defaults, options);
    
    this._container = container;
    this._panels = container.querySelectorAll("details");
    
    this.events = {
      openingPanel: new CustomEvent('openingPanel'),
      openedPanel: new CustomEvent('openedPanel'),
      closingPanel: new CustomEvent('closingPanel'),
      closedPanel: new CustomEvent('closedPanel'),
    };
  }  

  // Sets height of panel content
  _setPanelHeight( panel ) {
    let contents = panel.querySelector("summary + *");
    
    contents.style.height = contents.scrollHeight + "px";
  }

  // Removes height of panel content
  _removePanelHeight( panel ) {
    let contents = panel.querySelector("summary + *");
    
    contents.style.height = null;
  }
  
  //=== Open panel
  open(panel) {
    panel.dispatchEvent( this.events.openingPanel );

    panel.open = true;
  }

  // Add height and active class, this triggers opening animation
  _afterOpen(panel) {
    this._setPanelHeight(panel);
    panel.classList.add(this.settings.activeClass);
  }

  // Remove height on animation end since it's no longer needed
  _endOpen(panel) {
    panel.dispatchEvent( this.events.openedPanel );
    
    this._removePanelHeight(panel);
  }
  
  //=== Close panel, not toggling the actual [open] attr!
  close(panel) {
    panel.dispatchEvent( this.events.closingPanel );
    this._afterClose(panel);
  }
  
  // Set height, wait a beat, then remove height to trigger closing animation
  _afterClose(panel) {
    this._setPanelHeight(panel);

    setTimeout(() => {
      panel.classList.remove(this.settings.activeClass);
      this._removePanelHeight(panel);
    }, 100); //help, this is buggy and hacky
  }

  // Actually closes panel once animation finishes
  _endClose(panel) {
    panel.dispatchEvent( this.events.closedPanel );
    
    panel.open = false;
  }
  
  //=== Toggles panel... just in case anyone needs this
  toggle(panel) {
    panel.open ? this.close(panel) : this.open(panel);
  }

  //=== Accordion closes all panels except the current passed panel 
  openSinglePanel(panel) {
    this._panels.forEach((element) => {
      if (panel == element && !panel.open) {
        this.open(element);
      } else {
        this.close(element);
      }
    });
  }
  
  //=== Opens all panels just because
  openAll() {
    this._panels.forEach((element) => {
      this.open(element);
    });
  }
  
  //=== Closes all panels just in case
  closeAll() {
    this._panels.forEach((element) => {
      this.close(element);
    });
  }
  
  // Now put it all together
  _attachEvents() {
    this._panels.forEach(panel => {
      let toggler = panel.querySelector("summary");
      let contents = panel.querySelector("summary + *");

      // On panel open
      panel.addEventListener("toggle", e => {
        let isReadingHeight = panel.classList.contains(this.settings.heightClass);

        if (panel.open && !isReadingHeight) {
          this._afterOpen(panel);
        }
      });

      toggler.addEventListener("click", e => {
        // If accordion, stop default toggle behavior
        if (this.settings.accordion) {
          this.openSinglePanel(panel);
          e.preventDefault();
        }
        
        // On attempting close, stop default close behavior to substitute our own
        else if (panel.open) {
          this.close(panel);
          e.preventDefault();
        }
        
        // On open, proceed as normal (see toggle listener above)
      });
      
      /*
        transitionend fires once for each animated property, 
        but we want it to fire once for each click. 
        So let's make sure to watch only a single property
        Note this makes complex animations with multiple transition-durations impossible
        Sorry
      */
      let propToWatch = '';
          
      // On panel finishing open/close animation
      contents.addEventListener("transitionend", (e) => {
        // Ignore transitions from child elements
        if(e.target !== contents) {
          return;
        }
          
        // Set property to watch on first fire
        if ( !propToWatch ) propToWatch = e.propertyName;
        
        // If watched property matches currently animating property
        if ( e.propertyName == propToWatch ) {
          let wasOpened = panel.classList.contains(this.settings.activeClass);
          wasOpened ? this._endOpen(panel) : this._endClose(panel);
        }
      });
    });
  }

  init() {
    // Attach functionality
    this._attachEvents();
    
    // If accordion, open the first panel
    if (this.settings.accordion) {
      this.openSinglePanel(this._panels[0]);
    }
    
    // For styling purposes
    this._container.classList.add(this.settings.initClass);
    
    return this;
  }
}

let makeMePretty = document.querySelector(".collapse");
let accordion = new Collapse(makeMePretty, { accordion: true }).init();

// Toggle accordion behavior
document.querySelector("#accordion-toggle")
  .addEventListener("change", function() {
    this.checked ? 
      accordion.settings.accordion = false : 
      accordion.settings.accordion = true ;
});

// hoisthoistupwego I'm stuck on a machine with IE11
function miscPolyfillsForIE() {  
  // NodeList.forEach() polyfill
  // https://developer.mozilla.org/en-US/docs/Web/API/NodeList/forEach#Browser_Compatibility
  if (window.NodeList && !NodeList.prototype.forEach) {
    NodeList.prototype.forEach = Array.prototype.forEach;
  }

  // Object.assign() polyfill 
  // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign
  "function"!=typeof Object.assign&&Object.defineProperty(Object,"assign",{value:function(e,t){"use strict";if(null==e)throw new TypeError("Cannot convert undefined or null to object");for(var n=Object(e),r=1;r<arguments.length;r++){var o=arguments[r];if(null!=o)for(var c in o)Object.prototype.hasOwnProperty.call(o,c)&&(n[c]=o[c])}return n},writable:!0,configurable:!0});
  
  // CustomEvent polyfill
  // https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent
  !function(){if("function"==typeof window.CustomEvent)return!1;function t(t,e){e=e||{bubbles:!1,cancelable:!1,detail:void 0};var n=document.createEvent("CustomEvent");return n.initCustomEvent(t,e.bubbles,e.cancelable,e.detail),n}t.prototype=window.Event.prototype,window.CustomEvent=t}();
}

              
            
!
999px

Console