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HTML

              
                <h2>Hover Tabs</h2>
<p>Move the mouse over a button inside the tabbed menu:</p>

<div class="tab">
  <button class="tablinks" onmouseover="openCity(event, 'London')">London</button>
  <button class="tablinks" onmouseover="openCity(event, 'Paris')">Paris</button>
  <button class="tablinks" onmouseover="openCity(event, 'Tokyo')">Tokyo</button>
</div>

<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>

<div class="clearfix"></div>
              
            
!

CSS

              
                * {box-sizing: border-box}
body {font-family: "Lato", sans-serif;}

/* Style the tab */
.tab {
  float: left;
  border: 1px solid #ccc;
  background-color:#EBF4FA;
  width: 30%;
  height: 300px;
}

/* Style the buttons inside the tab */
.tab button {
  display: block;
  background-color: inherit;
  color: black;
  padding: 22px 16px;
  width: 100%;
  border: inherit;
  outline: none;
  text-align: left;
  cursor: pointer;
  font-size: 17px;
}

/* Change background color of buttons on hover */
.tab button:hover {
  background-color: #357EC7;
}

/* Create an active/current "tab button" class */
.tab button.active {
  background-color: #357EC7;
}

/* Style the tab content */
.tabcontent {
  float: left;
  padding: 0px 12px;
  border: 1px solid #ccc;
  width: 70%;
  background-color:#EBF4FA;
  border-left: none;
  height: 300px;
  display: none;
}

/* Clear floats after the tab */
.clearfix::after {
  content: "";
  clear: both;
  display: table;
}
              
            
!

JS

              
                function openCity(evt, cityName) {
  var i, tabcontent, tablinks;
  tabcontent = document.getElementsByClassName("tabcontent");
  for (i = 0; i < tabcontent.length; i++) {
    tabcontent[i].style.display = "none";
  }
  tablinks = document.getElementsByClassName("tablinks");
  for (i = 0; i < tablinks.length; i++) {
    tablinks[i].className = tablinks[i].className.replace(" active", "");
  }
  document.getElementById(cityName).style.display = "block";
  evt.currentTarget.className += " active";
}
              
            
!
999px

Console