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HTML

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HTML preprocessors can make writing HTML more powerful or convenient. For instance, Markdown is designed to be easier to write and read for text documents and you could write a loop in Pug.

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Adding Classes

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About the <head>

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Insecure Resource

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

It's a common practice to apply CSS to a page that styles elements such that they are consistent across all browsers. We offer two of the most popular choices: normalize.css and a reset. Or, choose Neither and nothing will be applied.

Vendor Prefixing

About Vendor Prefixing

To get the best cross-browser support, it is a common practice to apply vendor prefixes to CSS properties and values that require them to work. For instance -webkit- or -moz-.

We offer two popular choices: Autoprefixer (which processes your CSS server-side) and -prefix-free (which applies prefixes via a script, client-side).

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

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Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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Using packages here is powered by Skypack, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ES6 import usage.

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HTML 

              
                 
<div class="container">
 
    <ul class="tabs">
      <li class="current" rel="tab1">Tab 1</li>
      <li rel="tab2">Tab 2</li>
      <li rel="tab3">Tab 2</li>
    </ul>
 
   
    <div id="tab1" class="tab-container">
      
      <p>1. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec sed egestas felis. Etiam pellentesque auctor mi, a vestibulum elit sodales in. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Donec eget sollicitudin purus. Nam bibendum eget dolor eu viverra. Nulla tempor ante quis venenatis maximus. </p>
    </div>
    <div id="tab2" class="tab-container ">
      
      <p>2. Suspendisse in velit nibh. Vivamus in metus laoreet, feugiat neque in, tincidunt dolor. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum commodo, velit eu malesuada malesuada.</p>
    </div>
  
    <div id="tab3" class="tab-container">
      
      <p>3. Suspendisse in velit nibh. Vivamus in metus laoreet, feugiat neque in, tincidunt dolor. Orci varius natoque penatibus et magnis dis parturient montes, nascetur ridiculus mus. Vestibulum commodo, velit eu malesuada malesuada.</p>
    </div>
   
</div>
!

CSS 

              
                .container {
  width: 90%;
  max-width: 500px;
  margin: auto;
}

ul.tabs {
  margin: 0;
  padding: 0 0 12px 0;
  li {
    border: solid 1px #ccc;
    transition: all 0.3s ease-in-out;
    display: inline-block;
    padding: 10px 20px;
    cursor: pointer;
    &.current {
      background-color: #ccc;
    }
  }
}
 
.tab-container:not(.current){
  display: none;
   
}
!

JS 

              
                $(".tab-container:first").addClass("current");

$(".tabs li").click(function () {
  $(".tab-container").hide().removeClass("current");
  var activeTab = $(this).attr("rel");
  $("#" + activeTab)
    .fadeIn(1000)
    .addClass("current");

  $(".tabs li").removeClass("current");
  $(this).addClass("current");
});
!
999px

Console