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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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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

Any URL's added here will be added as <script>s in order, and run before the JavaScript in the editor. You can use the URL of any other Pen and it will include the JavaScript from that Pen.

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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.

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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 

              
                <h1>Light/Dark Toggle<br> Button</h1>

<div class="theme-toggle">
  <input type="checkbox" id="toggle-button" aria-label="Toggle Dark Mode">
  <label for="toggle-button">
    <i class="fas fa-moon" id="moon-icon"></i>
    <i class="fas fa-sun" id="sun-icon"></i>
  </label>
</div>
!

CSS 

              
                * {box-sizing: border-box;}

body {
  font-family: montserrat;
  text-align: center;
  transition: background 0.2s linear;
  height: 100vh; /* Added to ensure the body takes the full viewport height */
  display: flex; /* Added to create a flex container */
  flex-direction: column; /* Added to arrange content in a column */
  justify-content: center; /* Center horizontally */
  align-items: center; /* Center vertically */
  margin: 0; /* Added to remove default margin */
}

/* Hide the input checkbox */
#toggle-button {
  display: none;
}

/* Style for the moon and sun icons */
#moon-icon {
	color:black;
  transition: opacity 0.3s ease;
  font-size:50px;
  transform:translateX(25px);
}

#sun-icon {
	color:orange;
  transition: opacity 0.3s ease;
  opacity: 0;
  font-size:50px;
  transform:translateX(-25px);
}

/* When the checkbox is checked (i.e., dark theme is active), show the sun icon and hide the moon icon */
#toggle-button:checked + label #moon-icon {
  opacity: 0;
}

#toggle-button:checked + label #sun-icon {
  opacity: 1;
}

/* Optional: Style for the label itself (the clickable area) */
label {
  cursor: pointer;
}

/* Dark Theme Variants*/
body.dark-theme {
  background-color:black;
}

body.dark-theme h1 {
  color:white;
}
!

JS 

              
                // JavaScript
const toggleButton = document.getElementById('toggle-button');
const body = document.body;

// Check if a dark mode preference is stored in LocalStorage
const isDarkMode = localStorage.getItem('darkMode');

// Set the initial toggle state based on the stored preference
toggleButton.checked = isDarkMode === 'true';
body.classList.toggle('dark-theme', toggleButton.checked);

toggleButton.addEventListener('click', () => {
  const isDarkModeActive = body.classList.contains('dark-theme');
  
  // Toggle the class and store the dark mode preference in LocalStorage
  body.classList.toggle('dark-theme', !isDarkModeActive);
  localStorage.setItem('darkMode', !isDarkModeActive);
});
!
999px

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