CSS solution for light/dark/auto theme switcher for websites.
- It doesn’t have FART flash of light theme during JS initialization.
- Pure CSS solution. You need JS only to set HTML class, when user.
- Automatic theme provide better UX for users with theme switching by subset/sunrise (all operating systems now have theme switching schedule).
PostCSS plugin to make switcher to force dark or light theme by copying styles
from media query or light-dark() to special class.
/* Input CSS */
@media (prefers-color-scheme: dark) {
html {
--text-color: white
}
body {
background: black
}
}
section {
background: light-dark(white, black);
}/* Output CSS */
@media (prefers-color-scheme: dark) {
html:where(:not(.is-light)) {
--text-color: white
}
:where(html:not(.is-light)) body {
background: black
}
}
html:where(.is-dark) {
--text-color: white
}
:where(html.is-dark) body {
background: black
}
@media (prefers-color-scheme: dark) {
:where(html:not(.is-light)) section {
background: black;
}
}
:where(html.is-dark) section {
background: black;
}
@media (prefers-color-scheme: light) {
:where(html:not(.is-dark)) section {
background: white;
}
}
:where(html.is-light) section {
background: white;
}By default (without classes on html), website will use browser dark/light
theme. If user want to use dark theme, you set html.is-dark class.
If user want to force light theme, you use html.is-light.
Step 1: Install plugin:
npm install --save-dev postcss postcss-dark-theme-classStep 2: Check your project for existing PostCSS config: postcss.config.js
in the project root, "postcss" section in package.json
or postcss in bundle config.
If you do not use PostCSS, add it according to official docs and set this plugin in settings.
Step 3: Add the plugin to plugins list:
module.exports = {
plugins: [
+ require('postcss-dark-theme-class'),
require('autoprefixer')
]
}Step 4: Add theme switcher to UI. We recommend to have 3 states: light, dark, and auto.
Step 5: Set is-dark and is-light classes to <html> according
to switcher state:
<select name="themeSwitcher" id="themeSwitcher">
<option value="auto">Auto</option>
<option value="light">Light theme</option>
<option value="dark">Dark theme</option>
</select>const html = document.documentElement
const themeSwitcher = document.getElementById('themeSwitcher')
themeSwitcher.addEventListener('change', () => {
if (themeSwitcher.value === 'auto') {
html.classList.remove('is-dark', 'is-light')
} else if (themeSwitcher.value === 'light') {
html.classList.add('is-light')
html.classList.remove('is-dark')
} else if (themeSwitcher.value === 'dark') {
html.classList.add('is-dark')
html.classList.remove('is-light')
}
})Step 6: Save user’s choice in localStorage.
const html = document.documentElement
const themeSwitcher = document.getElementById('themeSwitcher')
themeSwitcher.addEventListener('change', () => {
+ localStorage.theme = themeSwitcher.value
if (themeSwitcher.value === 'auto') {
html.classList.remove('is-dark', 'is-light')
} else if (themeSwitcher.value === 'light') {
html.classList.add('is-light')
html.classList.remove('is-dark')
} else if (themeSwitcher.value === 'dark') {
html.classList.add('is-dark')
html.classList.remove('is-light')
}
})
+ if (localStorage.theme) {
+ themeSwitcher.value = localStorage.theme ?? "auto";
+ themeSwitcher.dispatchEvent(new Event("change"));
+ }Step 7: Think of adding a small inline JS to prevent FART completely.
<script>
if (localStorage.theme === 'light') {
html.classList.add('is-light')
} else if (localStorage.theme === 'dark') {
html.classList.add('is-dark')
}
</script>
</head>module.exports = {
plugins: [
require('postcss-dark-theme-class')({
darkSelector: '.dark-theme',
lightSelector: '.light-theme'
})
]
}Type: string. Default: .is-dark.
Any CSS’s valid selector for <html> (alias for :root), which will switch
dark theme. Use darkSelector: '[data-theme="dark"]' if you will switch theme
by setting <html data-theme=dark>
Type: string. Default: .is-light.
Any CSS’s valid selector, which will switch light theme.
Use lightSelector: '[data-theme="light"]' if you will switch theme by setting
<html data-theme="light">
Type: string[], string. Default: ['html', ':root'].
Selector for node for CSS Custom properties and dark/light theme classes.
Type: boolean. Default: true.
Should plugin wrap added selector to :where() to keep origin specificity.
Type: boolean. Default: false.
Should plugin remove origin @media and keep only classes. It could be useful
when only JS is responsible for theme switching.
If you are using this option, don’t forget:
- That theme should have 3 values: light, system, dark.
- To subscribe for system theme switching in JS.
We do not recommend this option for most of the cases, because of light flash when user visit your app with dark system theme and until JS will be loaded.
