This library is a port of next-themes for Svelte. All credit goes to pacocoursey and all next-themes contributors.

svelte-themes

An abstraction for themes in your Svelte app - works with any Svelte environment (SvelteKit, Vite, Webpack, etc.)

• ✅ Perfect dark mode in 2 lines of code
• ✅ System setting with prefers-color-scheme
• ✅ Themed browser UI with color-scheme
• ✅ No FOUC (Flash of Unstyled Content)
• ✅ Sync theme across tabs and windows
• ✅ Disable transition flash when changing themes
• ✅ Force pages to specific themes
• ✅ Class or data attribute selector
• ✅ Theme context
• ✅ Svelte 5 ready with modern runes syntax
• ✅ Universal - works with any Svelte setup
• ✅ SvelteKit dependency

Check out the Live Example to try it for yourself.

Install

$ pnpm add svelte-themes
# or
$ npm install svelte-themes
# or
$ yarn add svelte-themes

Using svelte-themes

Add SvelteTheme to your app's root component. In SvelteKit, this would be your +layout.svelte.

<!-- src/routes/+layout.svelte (SvelteKit) -->
<!-- or src/App.svelte (Vite + Svelte) -->

<script lang="ts">
	import { SvelteTheme } from 'svelte-themes';
	let { children } = $props();
</script>

<SvelteTheme>
	{@render children()}
</SvelteTheme>

Props

• storageKey = 'theme': Key used to store theme setting in localStorage
• defaultTheme = 'system': Default theme name. If enableSystem is false, the default theme is light
• forcedTheme: Forced theme name for the current page (does not modify saved theme settings)
• enableSystem = true: Whether to switch between dark and light based on prefers-color-scheme
• enableColorScheme = true: Whether to indicate to browsers which color scheme is used (dark or light) for built-in UI like inputs and buttons
• disableTransitionOnChange = false: Optionally disable all CSS transitions when switching themes
• themes = ['light', 'dark']: List of theme names
• attribute = 'data-theme': HTML attribute modified based on the active theme
  • accepts class and data-* (meaning any data attribute, data-mode, data-color, etc.)
• value: Optional mapping of theme name to attribute value
  • Example: { dark: 'dark-theme', light: 'light-theme' }
• colorScheme: Optional mapping of theme name to color scheme value
  • Example: { 'custom-dark': 'dark', 'custom-light': 'light' }

Reading and updating the theme

Use the useTheme() hook to access and change the active theme.

<script lang="ts">
  import { useTheme } from 'svelte-themes';
  const theme = useTheme();
</script>

<select bind:value={theme.theme}>
  {#each theme.themes as name (name)}
    <option value={name}>{name}</option>
  {/each}
</select>

<button onclick={() => (theme.theme = 'dark')}>Dark mode</button>
<button onclick={() => (theme.theme = 'light')}>Light mode</button>

Theme state

• theme: Active theme name
• resolvedTheme: If enableSystem is true and the active theme is "system", this returns whether the system preference resolved to "dark" or "light". Otherwise, identical to theme
• systemTheme: If enableSystem is true, represents the System theme preference ("dark" or "light"), regardless what the active theme is
• themes: The list of themes passed to SvelteTheme (with "system" appended, if enableSystem is true)

Examples

Basic dark/light mode

<script>
  import { SvelteTheme } from 'svelte-themes';
    let { children } = $props();
</script>

<SvelteTheme>
	{@render children()}
</SvelteTheme>

Custom theme names with value mapping

<script>
  import { SvelteTheme } from 'svelte-themes';
    let { children } = $props()
</script>

<SvelteTheme
  themes={['corporate', 'neon', 'vintage']}
  value={{
    corporate: 'theme-corporate',
    neon: 'theme-neon-bright',
    vintage: 'theme-retro'
  }}
  attribute="class"
>
	{@render children()}
</SvelteTheme>

With color scheme mapping

<script>
  import { SvelteTheme } from 'svelte-themes';
  let { children } = $props()
</script>

<SvelteTheme
  themes={['light', 'dark', 'midnight', 'dawn']}
  colorScheme={{
    midnight: 'dark',  // Maps to CSS color-scheme: dark
    dawn: 'light'      // Maps to CSS color-scheme: light
  }}
>
  {@render children()}
</SvelteTheme>