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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

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. So you don't have access to higher-up elements like the <html> tag. If you want to add classes there that can affect the whole document, this is the place to do it.

About the <head>

In CodePen, whatever you write in the HTML editor is what goes within the <body> tags in a basic HTML5 template. If you need things in the <head> of the document, put that code here.

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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.

Add External Scripts/Pens

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Packages

Add Packages

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 esm.sh, which makes packages from npm not only available on a CDN, but prepares them for native JavaScript ESM usage.

All packages are different, so refer to their docs for how they work.

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HTML 

              
                <div id="wrapper" class="loader">
  <h1>smiley face loader will remove itself after 3 seconds simulating load time</h1>
  <div id="wrapper-inner">
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam porttitor consectetur leo quis euismod. Mauris vulputate neque at ex tempor, ut fringilla mauris sagittis. Phasellus venenatis mi ut nulla tincidunt pulvinar. Pellentesque a ex et dolor
      aliquet consequat eget at mauris. Integer dolor ipsum, convallis quis magna sit amet, laoreet rhoncus nisl. Fusce commodo, arcu at tempus scelerisque, enim libero dignissim eros, sed sollicitudin velit metus et arcu. Proin quis egestas arcu, vitae
      rhoncus eros. Nunc bibendum semper lorem, in tincidunt felis.
      <br>
      <br> Morbi egestas nunc vel facilisis eleifend. Morbi sodales, massa sed iaculis ultricies, est elit malesuada lorem, ac scelerisque risus elit ut elit. Donec rutrum mattis sapien a feugiat. Nulla et libero in nisi dignissim tempor. Morbi dictum, mi
      quis tincidunt tempor, tortor mi egestas enim, et ullamcorper tortor est varius ante. Cras quis augue massa. Morbi ut turpis ultrices, aliquet magna ut, dignissim augue.
      <br>
      <br> Ut tempus tortor ut est pharetra sodales. In a cursus lectus, at tempor sem. Integer eu ligula at mi tristique ultricies ac et diam. Pellentesque gravida purus ligula, ac euismod massa accumsan vitae. Pellentesque aliquam lacus in tellus consectetur
      convallis. Nullam consectetur consectetur ligula, ut egestas turpis. Mauris finibus rhoncus erat, vel vehicula tortor feugiat nec. Proin ac nulla non nulla consequat fringilla. Quisque ac arcu semper, euismod quam at, malesuada lectus.
    <br><br>
    Lorem ipsum dolor sit amet, consectetur adipiscing elit. Etiam porttitor consectetur leo quis euismod. Mauris vulputate neque at ex tempor, ut fringilla mauris sagittis. Phasellus venenatis mi ut nulla tincidunt pulvinar. Pellentesque a ex et dolor
      aliquet consequat eget at mauris. Integer dolor ipsum, convallis quis magna sit amet, laoreet rhoncus nisl. Fusce commodo, arcu at tempus scelerisque, enim libero dignissim eros, sed sollicitudin velit metus et arcu. Proin quis egestas arcu, vitae
      rhoncus eros. Nunc bibendum semper lorem, in tincidunt felis.
      <br>
      <br> Morbi egestas nunc vel facilisis eleifend. Morbi sodales, massa sed iaculis ultricies, est elit malesuada lorem, ac scelerisque risus elit ut elit. Donec rutrum mattis sapien a feugiat. Nulla et libero in nisi dignissim tempor. Morbi dictum, mi
      quis tincidunt tempor, tortor mi egestas enim, et ullamcorper tortor est varius ante. Cras quis augue massa. Morbi ut turpis ultrices, aliquet magna ut, dignissim augue.
      <br>
      <br> Ut tempus tortor ut est pharetra sodales. In a cursus lectus, at tempor sem. Integer eu ligula at mi tristique ultricies ac et diam. Pellentesque gravida purus ligula, ac euismod massa accumsan vitae. Pellentesque aliquam lacus in tellus consectetur
      convallis. Nullam consectetur consectetur ligula, ut egestas turpis. Mauris finibus rhoncus erat, vel vehicula tortor feugiat nec. Proin ac nulla non nulla consequat fringilla. Quisque ac arcu semper, euismod quam at, malesuada lectus.</p>
  </div>
</div>
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CSS 

              
                html{
  height:100%;
}

body{
  height:100%;
  background:#666;
  overflow:hidden;
  font-size:14px;
}

h1 {
  font-weight:bold;
}

#wrapper{
  width:100%;
  height:100%; 
  text-align:center;
  color:#FFF;
}

#wrapper.loader {
  background: url("https://s3-us-west-2.amazonaws.com/s.cdpn.io/56901/smiley.gif") no-repeat 50% 46% transparent;
}

#wrapper-inner{
  font-size:20px;
  text-align:left;
  visibility:hidden;
}
!

JS 

              
                // wait until DOM is ready
$( document ).ready(function() {
   
    // wait until images, links, style-sheets, and other assets are loaded
    $( window ).load(function() { 
       
       // remove loader class
       // I use tweenmax delayedCall() instead of setTimout()
       // just so you can see the loader and see it removed
       // do not use for production 
       TweenMax.delayedCall(3, function(){
           $("#wrapper").removeClass("loader");
         
           TweenMax.to("#wrapper-inner",2,{autoAlpha:1})         
       });
      
       // your tweens
       

    });

});
!
999px

Console