Create simple tabs/tooltips within smooth animation using basic HTML, CSS, JS

simple-tabs.php

// #Step 1: HTML structure
<ul class="tab">
  <li><a href="javascript:void(0)" class="tablinks" onclick="openCity(event, 'London')">London</a></li>
  <li><a href="javascript:void(0)" class="tablinks" onclick="openCity(event, 'Paris')">Paris</a></li>
  <li><a href="javascript:void(0)" class="tablinks" onclick="openCity(event, 'Tokyo')">Tokyo</a></li>
</ul>

<div id="London" class="tabcontent">
  <h3>London</h3>
  <p>London is the capital city of England.</p>
</div>

<div id="Paris" class="tabcontent">
  <h3>Paris</h3>
  <p>Paris is the capital of France.</p> 
</div>

<div id="Tokyo" class="tabcontent">
  <h3>Tokyo</h3>
  <p>Tokyo is the capital of Japan.</p>
</div>

// #Step 2: CSS Structure
<style type="text/css">
  /* Style the list */
  ul.tab {
    list-style-type: none;
    margin: 0;
    padding: 0;
    overflow: hidden;
    border: 1px solid #ccc;
    background-color: #f1f1f1;
  }

  /* Float the list items side by side */
  ul.tab li {float: left;}

  /* Style the links inside the list items */
  ul.tab li a {
    display: inline-block;
    color: black;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    transition: 0.3s;
    font-size: 17px;
  }

  /* Change background color of links on hover */
  ul.tab li a:hover {background-color: #ddd;}

  /* Create an active/current tablink class */
  ul.tab li a:focus, .active {background-color: #ccc;}

  /* Style the tab content */
  .tabcontent {
    display: none;
    padding: 6px 12px;
    border: 1px solid #ccc;
    border-top: none;
  }
</style>

// #Step 3: Javascript Structure
<script type="text/javascript">
  function openCity(evt, cityName) {
    // Declare all variables
    var i, tabcontent, tablinks;

    // Get all elements with class="tabcontent" and hide them
    tabcontent = document.getElementsByClassName("tabcontent");
    for (i = 0; i < tabcontent.length; i++) {
        tabcontent[i].style.display = "none";
    }

    // Get all elements with class="tablinks" and remove the class "active"
    tablinks = document.getElementsByClassName("tablinks");
    for (i = 0; i < tablinks.length; i++) {
        tablinks[i].className = tablinks[i].className.replace(" active", "");
    }

    // Show the current tab, and add an "active" class to the link that opened the tab
    document.getElementById(cityName).style.display = "block";
    evt.currentTarget.className += " active";
  }
</script>

/** Optional Callback function **/
// #1, ADD ANIMATION FADED in tab transition. Please add these css line:
.tabcontent {
    -webkit-animation: fadeEffect 1s;
    animation: fadeEffect 1s; /* Fading effect takes 1 second */
}

@-webkit-keyframes fadeEffect {
    from {opacity: 0;}
    to {opacity: 1;}
}

@keyframes fadeEffect {
    from {opacity: 0;}
    to {opacity: 1;}
}

// #2, Shown a tab by default on page load. Add an id and stick it with click() function on page load:
<a href="javascript:void(0)" class="tablinks" onclick="openCity(event, 'London')" id="defaultOpen">London</a>
<script>
// Get the element with id="defaultOpen" and click on it
document.getElementById("defaultOpen").click();
</script>

// #3, Add a Close button to the tab content:
<!-- Click on the <span> element to close the tab -->
<div id="London" class="tabcontent">
  <h3>London</h3>
  <p>London is the capital city of England.</p>
  <span onclick="this.parentElement.style.display='none'">x</span> 
</div>

/** COPYRIGHTS **/
Thank to w3school.com! I was followed this: http://www.w3schools.com/howto/howto_js_tabs.asp
I just noted this snippet to my own notes for me easy to search.