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HTML

              
                <main>
  <article>
    <h1>Dark mode should be a user preference—not presumed</h1>
    <p>Yes, by default, when a user has <code>@media (prefers-color-scheme: dark)</code> set, we should set a dark theme, but we should also provide a switch for if the dark them isn’t working out for them.</p>
    <p>This also benefits users that don’t have <code>@media (prefers-color-scheme: dark)</code> set because they get a toggle to choose, too.</p>
  </article>
  <div class="user-toggle">
    <div role="status" class="[ visually-hidden ][ js-mode-status ]"></div>
    <button class="[ toggle-button ] [ js-mode-toggle ]">
      <span class="[ toggle-button__text ] [ js-mode-toggle-text ]">Enable dark mode</span>
      <span class="toggle-button__icon" aria-hidden="true"></span>
    </button>
  </div>
</main>
              
            
!

CSS

              
                :root {
  --color-mode: 'light';
  --color-dark: #141414;
  --color-dark-alpha: rgba(0, 0, 0, 0.1);
  --color-light: #efefef;
  --color-light-alpha: rgba(255, 255, 255, 0.9);
  
  /* https://twitter.com/Una/status/1129401554732277760 */
  --icon-sun: url('data:image/svg+xml,\
  <svg version="1.1" xmlns="http://www.w3.org/2000/svg" fill="currentColor" viewBox="0 0 24 24">\
    <path d="M18 12c0-0.811-0.161-1.587-0.455-2.295-0.304-0.735-0.75-1.395-1.303-1.948-0.552-0.552-1.213-0.998-1.948-1.303-0.707-0.293-1.483-0.454-2.294-0.454s-1.587 0.161-2.295 0.455c-0.735 0.304-1.395 0.75-1.948 1.302s-0.998 1.213-1.302 1.948c-0.294 0.708-0.455 1.484-0.455 2.295s0.161 1.587 0.455 2.295c0.304 0.735 0.75 1.395 1.303 1.948 0.552 0.552 1.213 0.998 1.948 1.303 0.707 0.293 1.483 0.454 2.294 0.454s1.587-0.161 2.295-0.455c0.735-0.304 1.395-0.75 1.948-1.303s0.998-1.213 1.303-1.948c0.293-0.707 0.454-1.483 0.454-2.294zM16 12c0 0.544-0.108 1.060-0.303 1.529-0.202 0.489-0.5 0.929-0.869 1.299s-0.81 0.667-1.299 0.869c-0.469 0.195-0.985 0.303-1.529 0.303s-1.060-0.108-1.529-0.303c-0.489-0.202-0.929-0.5-1.299-0.869s-0.667-0.81-0.869-1.299c-0.195-0.469-0.303-0.985-0.303-1.529s0.108-1.060 0.303-1.529c0.202-0.489 0.5-0.929 0.869-1.299s0.81-0.667 1.299-0.869c0.469-0.195 0.985-0.303 1.529-0.303s1.060 0.108 1.529 0.303c0.489 0.202 0.929 0.5 1.299 0.869s0.667 0.81 0.869 1.299c0.195 0.469 0.303 0.985 0.303 1.529zM11 1v2c0 0.552 0.448 1 1 1s1-0.448 1-1v-2c0-0.552-0.448-1-1-1s-1 0.448-1 1zM11 21v2c0 0.552 0.448 1 1 1s1-0.448 1-1v-2c0-0.552-0.448-1-1-1s-1 0.448-1 1zM3.513 4.927l1.42 1.42c0.391 0.391 1.024 0.391 1.414 0s0.391-1.024 0-1.414l-1.42-1.42c-0.391-0.391-1.024-0.391-1.414 0s-0.391 1.024 0 1.414zM17.653 19.067l1.42 1.42c0.391 0.391 1.024 0.391 1.414 0s0.391-1.024 0-1.414l-1.42-1.42c-0.391-0.391-1.024-0.391-1.414 0s-0.391 1.024 0 1.414zM1 13h2c0.552 0 1-0.448 1-1s-0.448-1-1-1h-2c-0.552 0-1 0.448-1 1s0.448 1 1 1zM21 13h2c0.552 0 1-0.448 1-1s-0.448-1-1-1h-2c-0.552 0-1 0.448-1 1s0.448 1 1 1zM4.927 20.487l1.42-1.42c0.391-0.391 0.391-1.024 0-1.414s-1.024-0.391-1.414 0l-1.42 1.42c-0.391 0.391-0.391 1.024 0 1.414s1.024 0.391 1.414 0zM19.067 6.347l1.42-1.42c0.391-0.391 0.391-1.024 0-1.414s-1.024-0.391-1.414 0l-1.42 1.42c-0.391 0.391-0.391 1.024 0 1.414s1.024 0.391 1.414 0z"></path>\
  </svg>');
  
  /* https://css-tricks.com/the-many-ways-to-change-an-svg-fill-on-hover-and-when-to-use-them/ */
  --icon-sun-filter: invert(0.61) sepia(0.8) saturate(5) hue-rotate(0deg) brightness(0.92);
  
  --icon-moon: url('data:image/svg+xml,\
  <svg version="1.1" xmlns="http://www.w3.org/2000/svg" fill="currentColor" viewBox="0 0 24 24">\
    <path d="M21.996 12.882c0.022-0.233-0.038-0.476-0.188-0.681-0.325-0.446-0.951-0.544-1.397-0.219-0.95 0.693-2.059 1.086-3.188 1.162-0.696 0.047-1.399-0.027-2.077-0.226-0.656-0.192-1.29-0.501-1.874-0.932-0.655-0.484-1.181-1.074-1.575-1.729-0.409-0.68-0.676-1.432-0.792-2.206s-0.082-1.571 0.11-2.342c0.184-0.741 0.514-1.46 0.999-2.115 0.142-0.191 0.216-0.435 0.191-0.691-0.053-0.55-0.542-0.952-1.092-0.898-1.117 0.109-2.186 0.399-3.172 0.843-1.005 0.452-1.925 1.065-2.723 1.808-0.883 0.82-1.618 1.801-2.159 2.901-0.523 1.064-0.863 2.238-0.978 3.485-0.125 1.347 0.024 2.658 0.402 3.878 0.392 1.266 1.031 2.431 1.863 3.433s1.86 1.843 3.033 2.461c1.13 0.595 2.392 0.982 3.739 1.106s2.659-0.025 3.878-0.403c1.266-0.392 2.431-1.031 3.433-1.863s1.843-1.86 2.461-3.033c0.595-1.13 0.982-2.392 1.106-3.739zM19.567 14.674c-0.126 0.351-0.276 0.689-0.447 1.014-0.493 0.937-1.166 1.76-1.969 2.427s-1.735 1.178-2.747 1.491c-0.973 0.302-2.021 0.421-3.102 0.321s-2.089-0.41-2.99-0.884c-0.937-0.493-1.76-1.166-2.427-1.969s-1.178-1.735-1.491-2.747c-0.302-0.973-0.421-2.021-0.321-3.102 0.092-1 0.365-1.938 0.782-2.786 0.43-0.878 1.018-1.661 1.725-2.319 0.64-0.595 1.377-1.086 2.183-1.449 0.179-0.081 0.362-0.155 0.548-0.223-0.092 0.257-0.171 0.516-0.236 0.778-0.256 1.029-0.302 2.091-0.147 3.121s0.51 2.032 1.056 2.941c0.527 0.875 1.23 1.663 2.1 2.306 0.775 0.573 1.622 0.986 2.5 1.243 0.907 0.266 1.846 0.364 2.772 0.302 0.752-0.050 1.496-0.207 2.21-0.465z"></path>\
  </svg>');
  --icon-moon-filter: invert(0.75);
  
  --background: #efefef;
  --text-color: #141414;
  --button-icon: var(--icon-moon);
  --button-icon-filter: var(--icon-moon-filter);
  --button-background: var(--color-dark);
  --button-color: var(--color-light);
  --border-color: var(--color-dark-alpha);
}

body {
  background: var(--background);
  color: var(--text-color);
  transition: background 500ms ease-in-out, color 200ms ease;
}

@media (prefers-color-scheme: dark) {
  :root {
    --color-mode: 'dark';
  }
  
  :root:not([data-user-color-scheme]) {
    --background: var(--color-dark);
    --text-color: var(--color-light);
    --button-icon: var(--icon-sun);
    --button-icon-filter: var(--icon-sun-filter);
    --button-background: var(--color-light);
    --button-color: var(--color-dark);
    --border-color: var(--color-light-alpha);
  }
}

[data-user-color-scheme="dark"] {
  --background: var(--color-dark);
  --text-color: var(--color-light);
  --button-icon: var(--icon-sun);
  --button-icon-filter: var(--icon-sun-filter);
  --button-background: var(--color-light-alpha);
  --button-color: var(--color-dark);
  --border-color: var(--color-light-alpha);
}

/* Remove _all_ animations and transitions for people that prefer not to see them */
@media (prefers-reduced-motion: reduce) {
  body {
    scroll-behavior: auto;
  }

  * {
    -webkit-animation: none !important;
    animation: none !important;
    transition: none !important;
  }
}

/* If there’s no JS, there’s no need for the user toggle component to show */
.no-js .user-toggle {
  display: none;
}

.user-toggle {
  margin: 2rem auto 0 auto;
  padding-top: 2.5rem;
  max-width: 20rem;
  border-top: 1px solid var(--border-color);
  text-align: center;
}

.toggle-button {
  display: inline-flex;
  background: var(--button-background);
  color: var(--button-color);
  border: none;
  font: inherit;
  font-size: 1.5rem;
  padding: 0.5rem 1rem;
  transition: background 500ms ease-in-out, color 200ms ease;
}

.toggle-button__icon {
  background: var(--button-icon);
  width: 1.2em; 
  height: 1.2em;
  margin: 0 0 0 0.5em;
  filter: var(--button-icon-filter);
  transform: translateY(1px); /* Optical adjustment */
  transition: filter 500ms ease-in-out;
}

.toggle-button:focus {
  outline: 1px solid var(--button-background);
  outline-offset: 0.5rem;
}










/* Presentational demo styles */

body {
  font-family: sans-serif;
  padding: 2rem 1rem;
  line-height: 1.4;
  display: grid;
  place-items: center;
}

article {
  max-width: 75ch;
  margin: 0 auto;
}

article > * + * {
  margin-top: 1em;
}

h1 {
  font-size: 2.5rem;
  line-height: 1.1;
}

p {
  font-size: 1.2rem;
  opacity: 0.9;
}

code {
  font-weight: 700;
  font-size: 1.3em;
  white-space: pre;
}

.visually-hidden { 
  display: block;
  height: 1px;
  width: 1px;
  overflow: hidden;
  clip: rect(1px 1px 1px 1px);
  clip: rect(1px, 1px, 1px, 1px);
  clip-path: inset(1px);
  white-space: nowrap;
  position: absolute;
}
              
            
!

JS

              
                // Remove the no JS class so that the button will show
document.documentElement.classList.remove('no-js');

const STORAGE_KEY = 'user-color-scheme';
const COLOR_MODE_KEY = '--color-mode';

const modeToggleButton = document.querySelector('.js-mode-toggle');
const modeToggleText = document.querySelector('.js-mode-toggle-text');
const modeStatusElement = document.querySelector('.js-mode-status');

/**
 * Pass in a custom prop key and this function will return its
 * computed value. 
 * A reduced version of this: https://andy-bell.design/wrote/get-css-custom-property-value-with-javascript/
 */
const getCSSCustomProp = (propKey) => {
  let response = getComputedStyle(document.documentElement).getPropertyValue(propKey);

  // Tidy up the string if there’s something to work with
  if (response.length) {
    response = response.replace(/\'|"/g, '').trim();
  }

  // Return the string response by default
  return response;
};

/**
 * Takes either a passed settings ('light'|'dark') or grabs that from localStorage.
 * If it can’t find the setting in either, it tries to load the CSS color mode,
 * controlled by the media query
 */
const applySetting = passedSetting => {
  let currentSetting = passedSetting || localStorage.getItem(STORAGE_KEY);
  
  if(currentSetting) {
    document.documentElement.setAttribute('data-user-color-scheme', currentSetting);
    setButtonLabelAndStatus(currentSetting);
  }
  else {
    setButtonLabelAndStatus(getCSSCustomProp(COLOR_MODE_KEY));
  }
}

/**
 * Get’s the current setting > reverses it > stores it
 */
const toggleSetting = () => {
  let currentSetting = localStorage.getItem(STORAGE_KEY);
  
  switch(currentSetting) {
    case null:
      currentSetting = getCSSCustomProp(COLOR_MODE_KEY) === 'dark' ? 'light' : 'dark';
      break;
    case 'light':
      currentSetting = 'dark';
      break;
    case 'dark':
      currentSetting = 'light';
      break;
  }


  localStorage.setItem(STORAGE_KEY, currentSetting);
  
  return currentSetting;
}

/**
 * A shared method for setting the button text label and visually hidden status element 
 */
const setButtonLabelAndStatus = currentSetting => { 
  modeToggleText.innerText = `Enable ${currentSetting === 'dark' ? 'light' : 'dark'} mode`;
  modeStatusElement.innerText = `Color mode is now "${currentSetting}"`;
}

/**
 * Clicking the button runs the apply setting method which grabs its parameter
 * from the toggle setting method.
 */
modeToggleButton.addEventListener('click', evt => {
  evt.preventDefault();
  
  applySetting(toggleSetting());
});

applySetting();
              
            
!
999px

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