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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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About External Resources

You can apply a script from anywhere on the web to your Pen. Just put a URL to it here and we'll add it, in the order you have them, before the JavaScript in the Pen itself.

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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About Packages

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.

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

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HTML 

              
                <!-- :valid -->
<section class="example-cntr validation valid">
    <h1>CSS <code>:valid</code> pseudo-class</h1>
    <p>The <code>:valid</code> pseudo-class targets form elements whose formatting is correct according to that element’s required format.</p>
    <p>In the following example, when the email input field has an email structure formatted correctly, the field it’s considered “valid” and a <span class="green">green</span> border appears around the input.</p>
    <p><em><span class="underline">Note:</span> In its default state, the field is considered valid. Not sure about you, but to me that feels counterintuitive :p</em></p>
    <label>
        <span>Email:</span>
        <input type="email" id="email" placeholder="[email protected]">
    </label>
</section>

<!-- :invalid -->
<section class="example-cntr validation invalid">
    <h1>CSS <code>:invalid</code> pseudo-class</h1>
    <p>The <code>:invalid</code> pseudo-class targets form elements whose formatting isn’t correct according to that element’s required format.</p>
    <p>In the following example, when the email input field has an incorrectly formatted email structure it’s automatically invalid and a <span class="red">red</span> border appears around the input.</p>
    <label>
        <span>Email:</span>
        <input type="email" id="email" placeholder="[email protected]">
    </label>
</section>
!

CSS 

              
                //'validations' generic styles
.validation {
    input[type=email] {
        box-sizing: content-box;
        width: 200px;
        padding: 0 5px;
        border: #666 5px solid;
        border-radius: 2px;
        cursor: text;
        transition: .5s;
    }
    label { display: inline-block; }
    span {
        display: block;
        margin-bottom: 5px;
    }
}

//:valid
.valid {
    input[type=email]:valid { border-color: $g; }
}
//:invalid
.invalid {
    input[type=email]:invalid { border-color: $r; }
}



//Styling stuff not needed for demo
body {
    text-align: left;
    line-height: 1.5;
}
h1 {
    font-size: 24px;
    text-transform: none;
    border-bottom: #636363 1px dotted;
    code {
        display: inline-block;
        margin-bottom: 10px;
        color: $y;
        background: none;
        box-shadow: none;
    }
}
code { font-size: 1em; }
input {
    width: 30px; height: 30px;
    vertical-align: middle;
    outline: none;
}
input, label { cursor: pointer; }
input[type=text],
input[type=email] { width: 100%; }

label {
    padding: 3px 8px 5px;
    border-radius: 2px;
    border: transparent 1px solid;    
    transition: .5s;
    &:hover {
        border: rgba(white,.2) 1px solid;        
    }
}
.example-cntr {
    max-width: 800px;
    margin: 0 auto 50px;
    padding: 30px;
    box-shadow: 0 1px 2px rgba(black,.3);
    background: rgba(black,.15);
}
.flex-ctnr {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
}

span {
    &.red,
    &.green,
    &.yellow {
        display: inline-block;
        font-weight: bold;
        font-size: 18px;
        text-shadow: 0 1px 0 #000;
    }
}
.underline { text-decoration: underline; }
.red { color: $r; }
.green { color: $g; }
.yellow { color: $y; }
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JS
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999px

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