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HTML 

              
                <main>
  <h1>HTML Buddies: <code>&lt;details&gt;</code> & <code>&lt;summary&gt;</code></h1>
  
    <p>
      These styles are not be beautiful because I made none. I <em>did</em>, however, take the time to do some digging to make sure your implementation is accessible. Then you can apply your techniques following best practices of making hover <em>and</em> focus styles, ensuring good contrast, and making sure you are not relying on color changes or visual cues alone.
  </p>
  
  <details>
  <summary>There is a polyfill…</summary>
    <p>
      Edge does not yet support <code>&lt;details&gt;</code> & <code>&lt;summary&gt;</code>, but <a href="https://github.com/javan/details-element-polyfill">with this polyfill</a> you can make Edge play along like the rest. The polyfill is embedded in this pen as well.
    </p>
    <p>
      Note that in all browsers that support <code>&lt;details&gt;</code> & <code>&lt;summary&gt;</code>, holding down the <kbd>Enter</kbd> key makes it toggle repeatedly, but not with the <kbd>Space</kbd> bar . The polyfill lets it toggle repeatedly with <kbd>Space</kbd> in Edge.
    </p>
</details>
  
  <details>
    <summary>…or you can detect support</summary>
    <p>
      Modernizr <a href="https://modernizr.com/download?details-setclasses">provides a configuration option</a> to detect whether a browser supports <code>&lt;details&gt;</code> & <code>&lt;summary&gt;</code>. Maybe do not use it if you are using the polyfill.
  </details>


  
  <h2>References</h2>
  
    <ul>
    <li>
      <a href="https://github.com/javan/details-element-polyfill">Polyfill</a> (or copy it out of the JS block of this pen).
    </li>
      
    <li>
      <a href="https://modernizr.com/download?details-setclasses">Modernizr feature detection</a>.
    </li>

    <li>
      This pen is for the May 2018 week 2 CodePen challenge, <a href="https://codepen.io/challenges/2018/may/">HTML Buddies</a>.
    </li>
    
    <li>
      You can see a <a href="https://blog.codepen.io/2018/05/20/codepenchallenge-details-and-summary-roundup/">round-up of week 2 on the CodePen blog</a>.
    
    <li>
      See <a href="http://adrianroselli.com/2018/06/codepen-html-buddies-challenge.html" target="_top">all four of my pens for this challenge</a> at my site with additional context.
    </li>
  </ul>

</main>
!

CSS 

              
                @import url('https://fonts.googleapis.com/css?family=Lato:400,700|VT323');

body {
  background-color: #8c90af;
  color: #333;
  font-family: Lato, Arial, sans-serif;
  padding: 0;
  margin: 0;
  line-height: 1.5;
}

li:not(:first-of-type) {
  margin-top: 1em;
}

code {
  font-family: 'VT323', 'Courier New', Courier, monospace;
  font-size: 110%;
  font-weight: normal;
  font-variant-ligatures: none;
  padding: 0.05em 0.25em;
  background-color: rgba(255, 255, 255, 0.75);
  border-radius: 0.5em;
}

main {
  display: block;
  box-sizing: border-box;
  width: 90%;
  margin: 1em auto;
  padding: 1em 2em;
  color: #000;
  background-color: rgba(255, 255, 255, 0.8);
  border: 0.07em solid rgba(0, 0, 0, 0.5);
  border-radius: 0.5em;
}

kbd		{	border: .07em solid #aaa;
			border-radius: 0.3em;
			box-shadow: 0.1em 0.2em 0.2em rgba(0,0,0,.5);
			background-color: #f9f9f9;
			background-image: linear-gradient(to bottom, #eee, #f9f9f9, #eee);
			padding: 0.1em 0.3em;
			font-family: Courier, "Courier New", monospace;
			font-size: 90%;
			color: #000;
			/* white-space: nowrap; */
			line-height: 1; }

code, kbd	{	box-decoration-break: slice;}

summary {
  font-weight: bold;
  margin: 0 0 0 -1em;
}

details {
  margin: 1em 1.5em;
}
!

JS 

              
                /*
Details Element Polyfill 2.0.1
Copyright © 2018 Javan Makhmali
 */
(function(){}).call(this),function(){var t,e,n,r,u,o,i,a,l,s,c,d;s={element:function(){var t,e,n,r,u;return e=document.createElement("details"),"open"in e?(e.innerHTML="<summary>a</summary>b",e.setAttribute("style","position: absolute; left: -9999px"),r=null!=(u=document.body)?u:document.documentElement,r.appendChild(e),t=e.offsetHeight,e.open=!0,n=e.offsetHeight,r.removeChild(e),t!==n):!1}(),toggleEvent:function(){var t;return t=document.createElement("details"),"ontoggle"in t}()},s.element&&s.toggleEvent||(i=function(){return document.head.insertAdjacentHTML("afterbegin",'<style>@charset"UTF-8";details:not([open])>*:not(summary){display:none;}details>summary{display:block;}details>summary::before{content:"\u25ba";padding-right:0.3rem;font-size:0.6rem;cursor:default;}details[open]>summary::before{content:"\u25bc";}</style>')},o=function(){var t,e,n,r;return e=document.createElement("details").constructor.prototype,r=e.setAttribute,n=e.removeAttribute,t=Object.getOwnPropertyDescriptor(e,"open"),Object.defineProperties(e,{open:{get:function(){var e;return"DETAILS"===this.tagName?this.hasAttribute("open"):null!=t&&null!=(e=t.get)?e.call(this):void 0},set:function(e){var n;return"DETAILS"===this.tagName?(e?this.setAttribute("open",""):this.removeAttribute("open"),e):null!=t&&null!=(n=t.set)?n.call(this,e):void 0}},setAttribute:{value:function(t,e){return d(this,function(n){return function(){return r.call(n,t,e)}}(this))}},removeAttribute:{value:function(t){return d(this,function(e){return function(){return n.call(e,t)}}(this))}}})},a=function(){return r(function(t){var e;return e=t.querySelector("summary"),t.hasAttribute("open")?(t.removeAttribute("open"),e.setAttribute("aria-expanded",!1)):(t.setAttribute("open",""),e.setAttribute("aria-expanded",!0))})},u=function(){var e,n,r,u,o;for(u=document.querySelectorAll("summary"),e=0,n=u.length;n>e;e++)o=u[e],t(o);return"undefined"!=typeof MutationObserver&&null!==MutationObserver?(r=new MutationObserver(function(e){var n,r,u,i,a;for(i=[],r=0,u=e.length;u>r;r++)n=e[r].addedNodes,i.push(function(){var e,r,u;for(u=[],e=0,r=n.length;r>e;e++)a=n[e],"DETAILS"===a.tagName&&(o=a.querySelector("summary"))?u.push(t(o,a)):u.push(void 0);return u}());return i}),r.observe(document.documentElement,{subtree:!0,childList:!0})):document.addEventListener("DOMNodeInserted",function(e){return"SUMMARY"===e.target.tagName?t(e.target):void 0})},t=function(t,e){return null==e&&(e=n(t,"DETAILS")),t.setAttribute("aria-expanded",e.hasAttribute("open")),t.hasAttribute("tabindex")||t.setAttribute("tabindex","0"),t.hasAttribute("role")?void 0:t.setAttribute("role","button")},l=function(){var t;return"undefined"!=typeof MutationObserver&&null!==MutationObserver?(t=new MutationObserver(function(t){var e,n,r,u,o,i;for(o=[],n=0,r=t.length;r>n;n++)u=t[n],i=u.target,e=u.attributeName,"DETAILS"===i.tagName&&"open"===e?o.push(c(i)):o.push(void 0);return o}),t.observe(document.documentElement,{attributes:!0,subtree:!0})):r(function(t){var e;return e=t.getAttribute("open"),setTimeout(function(){return t.getAttribute("open")!==e?c(t):void 0},1)})},e=function(t){return!(t.defaultPrevented||t.altKey||t.ctrlKey||t.metaKey||t.shiftKey||t.target.isContentEditable)},r=function(t){return addEventListener("click",function(r){var u,o;return e(r)&&r.which<=1&&(u=n(r.target,"SUMMARY"))&&"DETAILS"===(null!=(o=u.parentElement)?o.tagName:void 0)?t(u.parentElement):void 0},!1),addEventListener("keydown",function(r){var u,o,i;return e(r)&&(13===(o=r.keyCode)||32===o)&&(u=n(r.target,"SUMMARY"))&&"DETAILS"===(null!=(i=u.parentElement)?i.tagName:void 0)?(t(u.parentElement),r.preventDefault()):void 0},!1)},n=function(){return"function"==typeof Element.prototype.closest?function(t,e){return t.closest(e)}:function(t,e){for(;t;){if(t.tagName===e)return t;t=t.parentElement}}}(),c=function(t){var e;return e=document.createEvent("Events"),e.initEvent("toggle",!0,!1),t.dispatchEvent(e)},d=function(t,e){var n,r;return n=t.getAttribute("open"),r=e(),t.getAttribute("open")!==n&&c(t),r},s.element||(i(),o(),a(),u()),s.element&&!s.toggleEvent&&l())}.call(this),function(){}.call(this);
!
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