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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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If the script you link to has the file extension of a preprocessor, we'll attempt to process it before applying.

You can also link to another Pen here, and we'll pull the JavaScript from that Pen and include it. If it's using a matching preprocessor, we'll combine the code before preprocessing, so you can use the linked Pen as a true dependency.

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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 class="wrapper">
<div class="plus">
  <h2>Lorem ipsum dolor?</h2>
  <div class="hide">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Voluptates ducimus, cumque fugit harum voluptatum consectetur impedit ullam, et quisquam eum.</p>
    <p>Incidunt vel impedit accusantium voluptatum possimus maxime nesciunt, laboriosam iusto adipisci corporis, ab voluptatem natus nulla. Nisi quis repellendus at!</p>
  </div>
</div>
<div class="plus">
  <h2>Nisi ipsa facere?</h2>
  <div class="hide">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Soluta ipsam, voluptatum illum sed optio enim ea mollitia possimus accusantium animi.</p>
    <p>Qui, iure eius modi debitis, voluptates officia, animi inventore fugit accusantium sunt esse quos doloremque minima odit optio repellat in!</p>
  </div>
</div>
<div class="plus">
  <h2>Fuga atque voluptas?</h2>
  <div class="hide">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Ad suscipit ullam iure porro ab optio beatae eaque consequuntur dolor quos.</p>
    <p>Vitae, architecto, totam. Ad quas aut autem, voluptatem quibusdam voluptas vitae sed, tempora enim cum harum numquam blanditiis quod adipisci.</p>
  </div>
</div>
<div class="plus">
  <h2>Nemo nobis iusto?</h2>
   <div class="hide">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Officiis ratione, ut laborum quae. Laudantium incidunt, officia recusandae? Id, excepturi, sequi!</p>
    <p>Voluptatibus ducimus molestiae a, praesentium dignissimos optio culpa iusto, deleniti labore. Ullam assumenda, dicta nulla, voluptate quas possimus ut nemo!</p>
  </div>  
</div>
</div>
!

CSS 

              
                body {font: 14px Geneva, Verdana, sans-serif;}
.wrapper {
  width: 90%;
  margin: 20px auto;
}
.plus {
 background: url(https://html-plus.in.ua/wp-content/uploads/2016/04/plus.png) no-repeat 0 6px;
  padding: 10px;
  padding-left: 35px;
}
.minus {
 background: url(https://html-plus.in.ua/wp-content/uploads/2016/04/minus.png) no-repeat 0 6px;
  padding: 10px;
  padding-left: 35px;
}
.hide {display: none;}
.wrapper h2 {
  margin: 0;
  cursor: pointer;
}
!

JS 

              
                var change = document.getElementsByClassName("plus");
var len = change.length;
for(var i=0; i<len; i++){
  change[i].onclick = function(){
     this.classList.toggle("minus");
     this.children[1].classList.toggle("hide");
  }
}
!
999px

Console