Theme switcher

Four smooth ways to move between light and dark appearance.

import { ThemeSwitch } from "@/forma/arc/theme-switch/theme-switch";

Base

In FORMA

Liegt in kit/arc/theme-switch und ist über @/forma/arc/theme-switch/theme-switch erreichbar.
Farbe, Ecken, Höhen, Abstände, Tiefe, Schrift und Tempo kommen aus der Richtung (core/arc-bridge.ts); Arc behält Verhalten, Tastatur und Federn.

When to use

A single light and dark toggle in an app or marketing top bar.
Pages that want to run their own view transition from the button's position.

When not to use

Use user-menu when theme choice, including system, belongs inside an account menu.
Use theme-switch-rise for quiet product chrome, or theme-switch-eclipse for a dramatic showcase change.

Usage

import { ThemeSwitch } from "@/forma/arc/theme-switch/theme-switch";
import type { Theme } from "@/forma/arc/theme-switch/theme-switch";

export function AppearanceToggle({ theme, setTheme }: { theme: Theme; setTheme: (next: Theme) => void }) {
  return (
    <ThemeSwitch
      theme={theme}
      iconOnly
      onThemeChange={next => {
        if (!document.startViewTransition) return setTheme(next);
        document.startViewTransition(() => setTheme(next));
      }}
    />
  );
}

Examples

Reveal from the button

<ThemeSwitch
  theme={theme}
  onThemeChange={(next, _variant, trigger) => {
    const { left, top, width, height } = trigger.getBoundingClientRect();
    document.documentElement.style.setProperty("--x", `${left + width / 2}px`);
    document.documentElement.style.setProperty("--y", `${top + height / 2}px`);
    document.startViewTransition(() => setTheme(next));
  }}
/>

API reference

ThemeSwitch

A secondary Button that swaps a sun and moon icon and reports the next theme. The page transition itself is yours to run.

Prop	Type	Default	Description
`theme` (required)	`"light" \| "dark"`	–	The current theme. Drives the icon and aria-pressed.
`onThemeChange` (required)	`(next: Theme, variant: ThemeSwitchVariant, trigger: HTMLElement) => void`	–	Called on press with the opposite theme, the variant, and the button, so the page transition can start from it.
`variant`	`"reveal" \| "eclipse" \| "split" \| "rise"`	`"reveal"`	Names the page transition and sets the small icon nudge that matches it.
`label`	`string`	–	Accessible name. Defaults to "Switch to dark mode" or "Switch to light mode".
`iconOnly`	`boolean`	`false`	Hides the "Switch theme" text and renders a 38px square button.

Keyboard interactions

Keys	Action
Enter / Space	Toggles the theme.

Accessibility

Renders the library Button with aria-pressed set when the theme is dark.
aria-label defaults to "Switch to dark mode" or "Switch to light mode"; pass label to override.
The icons are aria-hidden.

Motion

Sun and moon trade places with a shared rotation, scale, and blur on a snappy spring; the icon also nudges in the direction of the chosen variant.
A theme that arrives during hydration swaps without motion, so a dark page never spins its switch on load.
Reduced motion swaps the icon with an instant fade and removes the nudge; skip the page transition too when reduced.

Responsive behavior

The labelled button fits a desktop top bar; pass iconOnly for a fixed 38px square on narrow headers and mobile.
Hover styles apply only on hover-capable fine pointers, so touch taps do not leave a stuck hover state.

Performance

The button itself is tiny: one icon swap on a spring, and the first theme after hydration applies without animating.
The page transition is yours; a full-page view transition snapshots the whole document, so keep it short and skip it for reduced motion.

Notes for AI

Use for a single light/dark toggle in a top bar. For light, dark, and system inside an account menu use user-menu.
The component only reports the change. Apply the theme in onThemeChange, typically inside document.startViewTransition, and use trigger's rect as the transition origin.
variant is passed back to onThemeChange so one handler can run the matching page transition (reveal, eclipse, split, rise).

Guidance for AI tools

Theme switcher: Four smooth ways to move between light and dark appearance. Follow the declared prop types and do not invent props. Keep keyboard access, reduced motion support, and both light and dark themes intact when adapting it.

Full library index: https://uiarc.dev/llms.txt

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Komponente und Text: Arc UI (MIT, uiarc.dev), angepasst für FORMA.