Create drop-down elements for html5 page

Directly from the official w3 page:

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i++) {
    acc[i].onclick = function(){
        this.classList.toggle("active");
        this.nextElementSibling.classList.toggle("show");
  }
}

button.accordion {
    background-color: #eee;
    color: #444;
    cursor: pointer;
    padding: 18px;
    width: 100%;
    border: none;
    text-align: left;
    outline: none;
    font-size: 15px;
    transition: 0.4s;
}

button.accordion.active, button.accordion:hover {
    background-color: #ddd;
}

button.accordion:after {
    content: '795';
    font-size: 13px;
    color: #777;
    float: right;
    margin-left: 5px;
}

button.accordion.active:after {
    content: "96";
}

div.panel {
    padding: 0 18px;
    background-color: white;
    max-height: 0;
    overflow: hidden;
    transition: 0.6s ease-in-out;
    opacity: 0;
}

div.panel.show {
    opacity: 1;
    max-height: 500px;
}

<h2>Accordion with symbols</h2>
<p>In this example we have added a "plus" sign to each button. When the user clicks on the button, the "plus" sign is replaced with a "minus" sign.</p>
<button class="accordion">Section 1</button>
<div class="panel">
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button class="accordion">Section 2</button>
<div class="panel">
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button class="accordion">Section 3</button>
<div id="foo" class="panel">
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

Nose if you have used Bootstrap , but otherwise, I recommend you use it, because one of the features it has, is to do exactly what you ask, I indicate the url where you can see the example in use: link

<div class="panel-group" id="accordion" role="tablist" aria-multiselectable="true">
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingOne">
      <h4 class="panel-title">
        <a role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseOne" aria-expanded="true" aria-controls="collapseOne">
          Collapsible Group Item #1
        </a>
      </h4>
    </div>
    <div id="collapseOne" class="panel-collapse collapse in" role="tabpanel" aria-labelledby="headingOne">
      <div class="panel-body">
        Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
      </div>
    </div>
  </div>
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingTwo">
      <h4 class="panel-title">
        <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseTwo" aria-expanded="false" aria-controls="collapseTwo">
          Collapsible Group Item #2
        </a>
      </h4>
    </div>
    <div id="collapseTwo" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingTwo">
      <div class="panel-body">
        Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
      </div>
    </div>
  </div>
  <div class="panel panel-default">
    <div class="panel-heading" role="tab" id="headingThree">
      <h4 class="panel-title">
        <a class="collapsed" role="button" data-toggle="collapse" data-parent="#accordion" href="#collapseThree" aria-expanded="false" aria-controls="collapseThree">
          Collapsible Group Item #3
        </a>
      </h4>
    </div>
    <div id="collapseThree" class="panel-collapse collapse" role="tabpanel" aria-labelledby="headingThree">
      <div class="panel-body">
        Anim pariatur cliche reprehenderit, enim eiusmod high life accusamus terry richardson ad squid. 3 wolf moon officia aute, non cupidatat skateboard dolor brunch. Food truck quinoa nesciunt laborum eiusmod. Brunch 3 wolf moon tempor, sunt aliqua put a bird on it squid single-origin coffee nulla assumenda shoreditch et. Nihil anim keffiyeh helvetica, craft beer labore wes anderson cred nesciunt sapiente ea proident. Ad vegan excepteur butcher vice lomo. Leggings occaecat craft beer farm-to-table, raw denim aesthetic synth nesciunt you probably haven't heard of them accusamus labore sustainable VHS.
      </div>
    </div>
  </div>
</div>

You can also do it with jquery: link

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>jQuery UI Accordion - Default functionality</title>
  <link rel="stylesheet" href="//code.jquery.com/ui/1.11.4/themes/smoothness/jquery-ui.css">
  <script src="//code.jquery.com/jquery-1.10.2.js"></script>
  <script src="//code.jquery.com/ui/1.11.4/jquery-ui.js"></script>
  <link rel="stylesheet" href="/resources/demos/style.css">
  <script>
  $(function() {
    $( "#accordion" ).accordion();
  });
  </script>
</head>
<body>

<div id="accordion">
  <h3>Section 1</h3>
  <div>
    <p>
    Mauris mauris ante, blandit et, ultrices a, suscipit eget, quam. Integer
    ut neque. Vivamus nisi metus, molestie vel, gravida in, condimentum sit
    amet, nunc. Nam a nibh. Donec suscipit eros. Nam mi. Proin viverra leo ut
    odio. Curabitur malesuada. Vestibulum a velit eu ante scelerisque vulputate.
    </p>
  </div>
  <h3>Section 2</h3>
  <div>
    <p>
    Sed non urna. Donec et ante. Phasellus eu ligula. Vestibulum sit amet
    purus. Vivamus hendrerit, dolor at aliquet laoreet, mauris turpis porttitor
    velit, faucibus interdum tellus libero ac justo. Vivamus non quam. In
    suscipit faucibus urna.
    </p>
  </div>
  <h3>Section 3</h3>
  <div>
    <p>
    Nam enim risus, molestie et, porta ac, aliquam ac, risus. Quisque lobortis.
    Phasellus pellentesque purus in massa. Aenean in pede. Phasellus ac libero
    ac tellus pellentesque semper. Sed ac felis. Sed commodo, magna quis
    lacinia ornare, quam ante aliquam nisi, eu iaculis leo purus venenatis dui.
    </p>
    <ul>
      <li>List item one</li>
      <li>List item two</li>
      <li>List item three</li>
    </ul>
  </div>
  <h3>Section 4</h3>
  <div>
    <p>
    Cras dictum. Pellentesque habitant morbi tristique senectus et netus
    et malesuada fames ac turpis egestas. Vestibulum ante ipsum primis in
    faucibus orci luctus et ultrices posuere cubilia Curae; Aenean lacinia
    mauris vel est.
    </p>
    <p>
    Suspendisse eu nisl. Nullam ut libero. Integer dignissim consequat lectus.
    Class aptent taciti sociosqu ad litora torquent per conubia nostra, per
    inceptos himenaeos.
    </p>
  </div>
</div>


</body>
</html>

I hope it serves you

An alternative without using JavaScript, only using HTML5 and CSS3. The idea is similar to that of this another question : use a hidden checkbox and a label, next to the previous selector ~ to show / hide the description to the question.

In normal state, the description is hidden, but when the checkbox is marked (thanks to label , without JavaScript), then the div that contains the answer to the question is displayed (making a selector as input:checked ~ div ).

Something like this:

.qa {
  margin-bottom:10px;  
}
.qa input {
  display:none;
}
.qa label {
  display:block;
  height:30px;
  line-height:30px;
  font-weight:bold;
  text-transform:uppercase;
}
.qa label:before {
  content:"+";
  display:inline-block;
  height:30px;
  width:30px;
  background:#ccc;
  color:White;
  text-align:center;
  margin-right:10px;
}
.qa div {
  display:none;
  padding-top:5px;
}
.qa input:checked ~ label:before {
  content:"-";
  background:#3a4;
}
.qa input:checked ~ div {
  display:block;
}

<div class="qa">
  <input type="checkbox" id="qa0" />
  <label for="qa0">Lorem ipsum dolor sit amet?</label>
  <div>
    Consectetur adipiscing elit. Nulla fermentum lacinia efficitur. Curabitur eget lobortis magna, eu placerat ligula. Integer commodo felis in nibh condimentum, at volutpat justo rhoncus. Vivamus eget est id tortor luctus dapibus in sed nisl. Aenean porttitor lacinia facilisis. Duis lobortis euismod ipsum, eget sodales ipsum efficitur vitae.
  </div>
</div>

<div class="qa">
  <input type="checkbox" id="qa1" />
  <label for="qa1">Aenean in mauris quis nisi ornare aliquet?</label>
  <div>
    Nulla dolor nulla, cursus non justo non, iaculis tempor tellus. Vestibulum scelerisque nisl eget erat dignissim, in laoreet diam auctor. Fusce rhoncus justo a ipsum elementum commodo. In et quam vel tortor commodo tempus. Fusce sem risus, euismod sit amet gravida nec, finibus quis lorem. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc gravida leo vel velit viverra commodo.
  </div>
</div>

One "drawback" of this solution is that it allows multiple questions to be open at the same time, although nothing is specified in the question about whether that is a requirement or not. Another drawback (this time without quotes) is that it is not easy to animate (it could be done with CSS transitions, but the ideal would be to pass height from 0 to auto and browsers do not support animations with auto ) .