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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.

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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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HTML 

              
                <button class="js__dark-mode-toggle dark-mode-toggle" type="button">
  <span class="dark-mode-toggle__icon"></span>
  <span class="dark-mode-toggle__text hidden--visually">dark mode</span>
</button>

<h1>Simple dark-mode toggle</h1>
<p>Switching dark mode with CSS custom properties and JavaScript.</p>
<p>Click the icon to switch modes.</p>

<pre><code>
&lt;button class="js__dark-mode-toggle dark-mode-toggle" type="button"&gt;
    &lt;span class="dark-mode-toggle__icon"&gt; &lt;/span&gt;
    &lt;span class="dark-mode-toggle__text hidden--visually"&gt;dark mode &lt;/span>
&lt;/button&gt;
</code></pre>
!

CSS 

              
                :root {
  --white: #fdfdfa;
  --black: #4d4d4d;
  --primary: #00b7c6;
  --grey--dark: #aca79a;
}

:root[data-theme="dark"] {
  --white: #4d4d4d;
  --black: #efeeeb;
  --primary: #ff851b;
}

body {
  font-size: 1rem;
  color: var(--black);
  background: var(--white);
  font-family: monospace;
  line-height: 1.7;
  padding: 4rem;
}

.dark-mode-toggle {
  appearance: none;
  -moz-appearance: none;
  -webkit-appearance: none;
  background: none;
  display: inline-block;
  border: none;
  border-radius: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 4rem;
  height: 4rem;
  cursor: pointer;
  overflow: hidden;
  border-radius: .4rem;
  border: .2rem solid var(--grey--dark);
}

.dark-mode-toggle:focus {
  outline: none;
  border-color: var(--primary);
}

:root[data-theme="dark"] .dark-mode-toggle__text:before {
  content: "deactivate ";
}

:root[data-theme="light"] .dark-mode-toggle__text:before {
  content: "activate ";
}

.dark-mode-toggle__icon {
  display: block;
  background: var(--grey--dark);
  border-radius: 50%;
  width: 2rem;
  height: 2rem;
  position: relative;
  transition: width 0.3s, height 0.3s;
  z-index: 1;
  transform: rotate(-20deg);
}

.dark-mode-toggle__icon:before {
  z-index: 0;
  content: "";
  position: absolute;
  display: block;
  border-right: none;
  border-radius: 50%;
  width: 2.4rem;
  height: 2.4rem;
  top: 50%;
  left: 50%;
  transition: opacity 0.3s, background-image 03s;
  opacity: 0;
  transform: translate(-50%, -50%) rotate(0deg);
  animation: spin__rays 4s linear infinite;
  background-image: linear-gradient(
      0deg,
      transparent 46%,
      var(--grey--dark) 46%,
      var(--grey--dark) 54%,
      transparent 54%
    ),
    linear-gradient(
      90deg,
      transparent 46%,
      var(--grey--dark) 46%,
      var(--grey--dark) 54%,
      transparent 54%
    ),
    linear-gradient(
      45deg,
      transparent 47%,
      var(--grey--dark) 47%,
      var(--grey--dark) 53%,
      transparent 53%
    ),
    linear-gradient(
      135deg,
      transparent 47%,
      var(--grey--dark) 47%,
      var(--grey--dark) 53%,
      transparent 53%
    );
}

.dark-mode-toggle__icon:after {
  content: "";
  position: absolute;
  display: block;
  background: var(--white);
  border-radius: 0.7rem;
  width: 1.4rem;
  height: 1.4rem;
  top: 50%;
  left: 200%;
  transform: translateY(-50%);
  transition: left 0.3s;
}

.dark-mode-toggle:hover .dark-mode-toggle__icon {
  background: var(--primary);
}
.dark-mode-toggle:hover .dark-mode-toggle__icon:before {
  background-image: linear-gradient(
      0deg,
      transparent 47%,
      var(--primary) 47%,
      var(--primary) 53%,
      transparent 53%
    ),
    linear-gradient(
      90deg,
      transparent 47%,
      var(--primary) 47%,
      var(--primary) 53%,
      transparent 53%
    ),
    linear-gradient(
      45deg,
      transparent 48%,
      var(--primary) 48%,
      var(--primary) 52%,
      transparent 52%
    ),
    linear-gradient(
      135deg,
      transparent 48%,
      var(--primary) 48%,
      var(--primary) 52%,
      transparent 52%
    );
}

:root[data-theme="light"] .dark-mode-toggle__icon:after {
  left: 40%;
}
:root[data-theme="dark"] .dark-mode-toggle__icon {
  width: 1.6rem;
  height: 1.6rem;
}
:root[data-theme="dark"] .dark-mode-toggle__icon:before {
  opacity: 1;
}

@keyframes spin__rays {
  from {
    transform: translate(-50%, -50%) rotate(0deg);
  }
  to {
    transform: translate(-50%, -50%) rotate(90deg);
  }
}

/* Hide only visually, but have it available for screenreaders */
.hidden--visually {
  border: 0;
  clip: rect(0 0 0 0);
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0;
  position: absolute;
  width: 1px;
}
!

JS 

              
                // Note: CodePen does not allow use of local
// storage (for sensible security reasons).
// If you're adding this code to your own site,
// reinstate the commented-out lines and the
// code will work fully.

const setDarkMode = (active = false) => {
  const wrapper = document.querySelector(":root");
  if (active) {
    wrapper.setAttribute("data-theme", "dark");
    // localStorage.setItem("theme", "dark");
  } else {
    wrapper.setAttribute("data-theme", "light");
    // localStorage.setItem("theme", "light");
  }
};

const toggleDarkMode = () => {
  const theme = document.querySelector(":root").getAttribute("data-theme");
  // If the current theme is "light", we want to activate dark
  setDarkMode(theme === "light");
};

const initDarkMode = () => {
  const query = window.matchMedia("(prefers-color-scheme: dark)");
  // const themePreference = localStorage.getItem("theme");

  let active = query.matches;
  // if (themePreference === "dark") {
  //   active = true;
  // }
  // if (themePreference === "light") {
  //   active = false;
  // }

  setDarkMode(active);

  query.addListener(e => setDarkMode(e.matches));

  const toggleButton = document.querySelector(".js__dark-mode-toggle");
  toggleButton.addEventListener("click", toggleDarkMode);
};

initDarkMode();
!
999px

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