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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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HTML 

              
                <div class="cards">
    <div class="card">
        <h2 class="title">Card 1</h2>
        <div class="text">Lorem ipsum dolor sit amet, consectetur adipisicing elit. Hic magnam, itaque obcaecati, dolorum odio voluptate ratione doloribus ipsa voluptates ipsam, repellat labore voluptatum iure recusandae mollitia impedit delectus? Odit, rerum!</div>
    </div>
    <div class="card">
        <h2 class="title">Card 2</h2>
        <div class="text">Numquam fugiat rerum tempora facilis perferendis facere, ex, iusto accusamus provident molestiae temporibus reprehenderit. Accusantium sequi impedit a, ea harum perferendis deleniti nulla ex, deserunt similique adipisci. Possimus, quibusdam, amet.</div>
    </div>
    <div class="card">
        <h2 class="title">Card 3</h2>
        <div class="text">Distinctio quibusdam similique temporibus, molestias accusamus architecto in. Commodi labore laboriosam velit provident adipisci aspernatur vel facilis, iusto cupiditate repudiandae molestiae, perferendis nobis nemo, et praesentium at illo neque maxime.</div>
    </div>
    <div class="card">
        <h2 class="title">Card 4</h2>
        <div class="text">Inventore quo molestias, laborum labore eligendi voluptatibus dolore aliquam enim, amet ipsum dolorem. Molestiae quidem, fugit! Ad, illum, impedit. Eveniet necessitatibus delectus repellat, nobis esse quidem neque, officia mollitia cumque.</div>
    </div>
    <div class="card">
        <h2 class="title">Card 5</h2>
        <div class="text">Harum ad nostrum neque quaerat expedita ea quos necessitatibus praesentium dolorum eius consequatur, ullam fugit, saepe doloribus vel consectetur! Dolore nihil deleniti autem maiores possimus incidunt nisi recusandae maxime eius.</div>
    </div>
    <div class="card">
        <h2 class="title">Card 6</h2>
        <div class="text">Iste animi ducimus laborum culpa, excepturi in quo dolorum quasi expedita, mollitia cupiditate. Aperiam neque mollitia animi sapiente ab officiis, tempora voluptatem. Cumque, facilis. Dolores saepe asperiores doloremque illo unde!</div>
    </div>
    <div class="card">
        <h2 class="title">Card 7</h2>
        <div class="text">Commodi explicabo, accusamus ipsum reprehenderit recusandae doloribus dicta. Quam maiores eos tempora voluptatem placeat laboriosam et expedita nostrum eius vitae dignissimos non, architecto sint deleniti autem nam molestiae eligendi facere?</div>
    </div>
    <div class="card">
        <h2 class="title">Card 8</h2>
        <div class="text">Reiciendis saepe dolore quisquam quod earum, illum iste tenetur, maxime nihil enim similique necessitatibus nemo harum rerum sed vero dolorum eius quia quasi incidunt sint culpa labore non quas! Aperiam.</div>
    </div>
    <div class="card">
        <h2 class="title">Card 9</h2>
        <div class="text">Repudiandae, nisi, quibusdam? Iusto architecto adipisci, quisquam, maiores minus perferendis eligendi maxime similique molestias qui quasi porro aperiam deserunt. Odit, id deserunt illum nobis maiores labore earum rem obcaecati aspernatur?</div>
    </div>
    <div class="card">
        <h2 class="title">Card 10</h2>
        <div class="text">Quasi cupiditate illo officia minima fugiat omnis impedit ullam, temporibus modi atque quod, accusantium pariatur sit, facilis vero! Magnam laudantium sapiente, eum. Animi inventore sed aut aliquid deleniti amet asperiores.</div>
    </div>
</div>
!

CSS 

              
                html {
    padding: 20px;
}

.card {
    max-width: 300px;
    margin: 0 auto 10px;
    padding: 20px;
    background: beige;
    box-shadow: 1px 1px gray;
    pointer: cursor;
}

.card > .title {
    margin: 0;
}

.card > .text {
    display: none;
    margin-top: 10px;
    padding-top: 10px;
    border-top: 1px solid #ddd;
}

.card.active > .text,
.card.show-content > .text {
    display: block;
}
!

JS 

              
                $( window ).ready( function() {
    var cards = $( '.card' );
    
    cards.click( function() {
        var timeToShow = false;

        cards
            .removeClass( 'active' )
            .removeClass( 'show-content' );
        
        $( this ).addClass( 'active' );

        cards.each( function() {
            var currentCard = $( this );
            if ( timeToShow ) {
                currentCard.addClass( 'show-content' );
            }
            if ( currentCard.hasClass( 'active' ) ) {
                timeToShow = true;
            }
        } );
        
    } );
    
} );
!
999px

Console