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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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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

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.

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HTML 

              
                <div class="wrapper">
  <section>
    <h2>Accordion with HTML/CSS</h2>
    <div class="accordion">
      <details>
        <summary>Section 1</summary>
        <p>This is the content for section 1.</p>
      </details>
      <details>
        <summary>Section 2</summary>
        <p>This is the content for section 2.</p>
      </details>
      <details>
        <summary>Section 3</summary>
        <p>This is the content for section 3.</p>
      </details>
    </div>
  </section>

  <section>
    <h2>Accordion with Javascript</h2>
    <div class="accordion">
      <div class="accordion-item">
        <div class="accordion-header">Section 1</div>
        <div class="accordion-content">
          <p>This is the content for section 1.</p>
        </div>
      </div>
      <div class="accordion-item">
        <div class="accordion-header">Section 2</div>
        <div class="accordion-content">
          <p>This is the content for section 2.</p>
        </div>
      </div>
      <div class="accordion-item">
        <div class="accordion-header">Section 3</div>
        <div class="accordion-content">
          <p>This is the content for section 3.</p>
        </div>
      </div>
    </div>
  </section>
</div>
!

CSS 

              
                .wrapper {
  display: flex;
  gap: 10px;
}

section {
  width: 50%;
  border: 1px solid grey;
  padding: 50px;
}
@media screen and (max-width: 960px) {
  .wrapper {
    flex-direction: column;
  }
  section {
    width: calc(100% - 100px);
  }
}

/* html/css implementation */
.accordion {
  width: 100%;
  max-width: 600px;
  margin: 0 auto;
}

summary {
  padding: 15px;
  background-color: #f1f1f1;
  cursor: pointer;
  font-weight: bold;
  border: 1px solid #ccc;
  /* Remove the default arrow icon */
  list-style: none;
  appearance: none;
  -webkit-appearance: none;
  -moz-appearance: none;
}

details[open] summary {
  /* Add custom styling for open state */
  background-color: #e0e0e0;
}

details {
  border: 1px solid #ccc;
  margin-bottom: 5px;
}

details p {
  padding: 15px;
  background-color: #fff;
}

/* js implementation */
.accordion {
  width: 100%;
  max-width: 600px;
  margin: 0 auto;
}

.accordion-item {
  border: 1px solid #ccc;
  margin-bottom: 5px;
}

.accordion-header {
  padding: 15px;
  background-color: #f1f1f1;
  cursor: pointer;
  font-weight: bold;
}

.accordion-content {
  display: none;
  padding: 15px;
  background-color: #fff;
}
!

JS 

              
                document.querySelectorAll(".accordion-header").forEach((header) => {
  header.addEventListener("click", () => {
    const content = header.nextElementSibling;
    content.style.display = content.style.display === "none" ? "block" : "none";
  });
});
!
999px

Console