<div id="container">
  <div aria-hidden="true" id="note">
    Below is the article made with a bunch of non-semantic (<code>&lt;div&gt;</code>) elements. Try adding this <a href="https://chrome.google.com/webstore/detail/screen-reader/kgejglhpjiefppelpmljglcjbhoiplfn/related?hl=en" target="_blank">Screen Reader extension</a> and interact with it using your keyboard (tab, space,...) or mouse. 
  </div>
  
  <div role="button" aria-label="Toggle theme" aria-pressed="false" id="themeBtn" onClick="toggleTheme()" tabindex="0">Dark theme</div>

  <div role="article" aria-label="Main" id="article">
    <div role="heading" aria-level="1" tabindex="0">Title</div>

    <div role="heading" aria-level="2" tabindex="0">Introduction</div>
    <div role="paragraph" aria-label="Paragraph collapsed" aria-expanded="false" tabindex=0 id="paragraph">
      Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus imperdiet, nulla et dictum interdum, nisi lorem egestas vitae scel erisque enim ligula venenatis dolor<span id="dots" aria-hidden="true">...</span><span id="more" aria-hidden="true">. Maecenas nisl est, ultrices nec congue eget, auctor vitae massa. Fusce luctus vestibulum augue ut aliquet. Nunc sagittis dictum nisi, sed ullamcorper ipsum dignissim ac. In at libero sed nunc venenatis imperdiet sed ornare turpis. Donec vitae dui eget tellus gravida venenatis. Integer fringilla congue eros non fermentum. Sed dapibus pulvinar nibh tempor porta.
    </div>
    <div role="button" aria-label="Read more" aria-expanded="false" onclick="toggleReadMore()" id="readMoreBtn" tabindex=0>Read more</div>

    <div role="heading" aria-level="2" tabindex="0">Chapter 1</div>
    <div role="heading" aria-level="3" tabindex="0">Chapter 1.1</div>
    <div role="heading" aria-level="3" tabindex="0">Chapter 1.2</div>
    <div role="heading" aria-level="2" tabindex="0">Chapter 2</div>

    <div role="navigation" id="navigation">
      <a role="button" aria-label="Previous" aria-disabled="true" tabindex="0">
        &lsaquo;
      </a>

      <a role="button" aria-label="Next" aria-disabled="false" tabindex="0">
        &rsaquo;
      </a>
    </div>
  </div>
</div>

:root {
  --bg-light: #FFF;
  --txt-light: #333;
  --bg-dark: #111;
  --txt-dark: #EEE;
}

*{
  padding: 0;
  margin: 0;
}

#container{
  padding: 20px;
  height: max-content;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}

#note{
  margin-bottom: 10px;
  width: 75%;
  max-width: 600px;
}

[role="article"]{
  border: 1px solid #BBB;
  padding: 10px;
  width: 75%;
  max-width: 600px;
  color: var(--tx-light);
}

[role="heading"]{
  font-weight: bold;
}

#paragraph{
  text-align: justify;
}

#more{
  display: none;
}

[aria-level="1"]{
  font-size: 21px;
  text-transform: uppercase;
  width: 100% !important;
  text-align: center;
}

[aria-level="2"]{
  font-size: 19px;
  width: max-content;
  margin-top: 5px;
}

[aria-level="3"]{
  width: max-content;
  margin-left: 10px;
  font-size: 18px;
}

[aria-level="3"]:before{
  content: '\25CF';
  margin-right: 5px;
}

[role="navigation"]{
  display: flex;
  justify-content: space-between;
  width: 100%;
  margin-top: 10px;
}

[role="button"] {
  cursor: pointer;
  width: max-content;
  font-size: 28px;
  font-weight: bold;
  padding: 0 12px;
  border-radius: 5px;
  box-shadow: 0 1px 2px #0007;
  color: #FFF;
  text-shadow: -1px -1px 1px #888;
  background-image: linear-gradient(
    to bottom,
    #FFF,
    #CCC
  );
}

[role="button"]:hover {
  background-image: linear-gradient(
    to bottom,
    #EEE,
    #BBB
  );
}

[aria-label="Read more"],
[aria-label="Toggle theme"]{
  font-size: 16px;
  text-shadow: none;
  font-weight: normal;
  color: #333;
  padding: 3px 5px;
}

[aria-label="Toggle theme"]{
  margin: 0px 0px 5px;
}

[aria-label="Read more"]{
  margin: 5px 0px;
}

[aria-label="Toggle theme"][aria-pressed="true"]{
  box-shadow: inset 0 1px 2px #0007;
}

[aria-disabled="true"] {
  cursor: not-allowed;
  box-shadow: none;
  background-image: linear-gradient(
    to bottom,
    #F8F8F8,
    #E8E8E8
  );
}

[aria-disabled="true"]:hover {
  background-image: linear-gradient(
    to bottom,
    #F8F8F8,
    #E8E8E8
  );
}

const ellipsis = document.getElementById("dots");
const hiddenContent = document.getElementById("more");
const readMoreBtn = document.getElementById("readMoreBtn");
const paragraph = document.getElementById("paragraph");
const themeBtn = document.getElementById("themeBtn");
const article = document.getElementById("article");

function toggleReadMore() {
  if (event.keyCode === 32 || event.keyCode === 13) {
    event.preventDefault();
  }
  if(event.keyCode !== 9 && event.keyCode !== 16){
    if (ellipsis.style.display === "none") {
      ellipsis.style.display = "inline";
      readMoreBtn.innerHTML = "Read more"; 
      readMoreBtn.setAttribute('aria-expanded', 'false');
      hiddenContent.style.display = "none";
      paragraph.setAttribute('aria-label', 'Paragraph collapsed');
    } else {
      ellipsis.style.display = "none";
      readMoreBtn.innerHTML = "Read less"; 
      readMoreBtn.setAttribute('aria-expanded', 'true');
      hiddenContent.style.display = "inline";
      paragraph.setAttribute('aria-label', 'Paragraph expanded');
    }
  }
}

let isLightTheme = true
function toggleTheme() {
  if (event.keyCode === 32 || event.keyCode === 13) {
    event.preventDefault();
  }
  if(event.keyCode !== 9 && event.keyCode !== 16){
    isLightTheme = !isLightTheme

    themeBtn.setAttribute('aria-pressed', isLightTheme? 'false' : 'true')
    if(isLightTheme){
      article.style.color = 'var(--txt-light)';
      article.style.backgroundColor = 'var(--bg-light)';
    } else {
      article.style.color = 'var(--txt-dark)';
      article.style.backgroundColor = 'var(--bg-dark)';
    }
  }
}

readMoreBtn.addEventListener('keydown', toggleReadMore);
themeBtn.addEventListener('keydown', toggleTheme);
// readMoreBtn.addEventListener('keyup', toggleReadMore);