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HTML

About HTML Preprocessors

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).

Add External Stylesheets/Pens

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

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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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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 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 

              
                <body>
  <main>
    <h1>A More Accessible Required Field</h1>
    
    <form class="flow">
      <fieldset class="example example__bad">
        <legend>Visible indication only</legend>
        
        <!-- A common convention is to use an asterix (*) next to a label to indicate required fields. But this doesn't programatically indicate the field is required and depending on screen reader settings, it may not announce the asterix at all -->
        <label for="name1">Name *</label>
        <input type="text" id="name1">
        <small>All fields marked with * are required</small>
      </fieldset>
      
      <fieldset class="example example__bad">
        <legend>Relying on color only</legend>
        
        <!-- Sometimes color or bolder borders are used to indicate whether a field is required. This technique doesn't programtically indicate that a field is required, and the visual cues can also be missed by users with low contrast or color visibility issues. -->
        <label for="name2" class="required">Name</label>
        <input type="text" id="name2">
      </fieldset>
      
      <fieldset class="example example__bad">
        <legend>Programtically setting required fields</legend>
        
        <!-- Using the HTML5 required attribute will announce the field as required to screen readers, but doesn't provide any visual feedback about the required state. To stop screen readers from announcing required fields as invalid by default, set the aria-invalid="false" attribute. -->
        <label for="name3">Name</label>
        <input type="text" id="name3" required aria-invalid="false">
      </fieldset>
      
      <fieldset class="example example__good">
        <legend>Putting it All Together</legend>
        
        <!-- Using the HTML5 required attribute in addition to visual cues ensure all users know if a field is required or not. -->
        <label for="name4">Name *</label>
        <input type="text" id="name4" required aria-invalid="false">
        <small>All fields marked with * are required</small>
      </fieldset>
    </form>
  </main>
</body>
!

CSS 

              
                :root {
  --space: 1.5rem;
}

body {
  background-color: #bebebe;
  display: grid;
  place-items: center;
  align-items: center;
  padding: var(--space);
}

main {
  background-color: #fefefe;
  padding: calc(var(--space) * 2);
  max-width: 70ch;
  border-radius: 0.25rem;
}

.flow > * + * {
  margin-top: var(--space);
}

article {
  margin-top: 3rem;
}

input {
  border-radius: 0.25rem;
  padding: 0.5rem;
}

.example {
  outline: 1px solid #efefef;
  padding: 1rem;
  border-left: 4px solid;
}

.example__bad {
  border-left-color: red;
}

.example__good {
  border-left-color: green;
}

.example__goodinput[required] input[required] {
  border: 2px solid #222;
}

label + input[type="text"] {
  display: block;
}

/* Utility Classes */

.required {
  color: red;
}

.required + input {
  background-color: #efefef;
}

.d-block {
  display: block;
}

.txt-small {
  font-size: 90%;
}

.txt-light {
  color: #444444;
}
!

JS
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999px

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