Theming

@sometic/theme is the runtime design-token and theme engine for Sometic. It owns token maps, CSS variable generation, system preference detection, WCAG contrast helpers (hex today), light/dark presets, and a framework-neutral theme controller that produces a stable ThemeSnapshot you can bind in any UI stack.

System standout: contrast, scoped brand, color-scheme

Applies CSS color-scheme with data-color-scheme. Use auditThemeContrast / assertThemeContrast, createScopedThemeController, and defineSemanticTokens. Sync document head via bindThemeToHead.

This section is the consumer guide for theming. Preference persistence lives on the Theme store bridge page; the underlying store primitives are documented under Store.

Overview

Sometic theming is behavior first, not a shipped visual kit:

• You define tokens (color, space, radius, or your own categories).
• The controller resolves mode, theme id, density, direction, high contrast, and reduced motion into one snapshot.
• You apply that snapshot to document.documentElement or any scoped element via applyThemeToElement.
• Your CSS (plain, Tailwind, Bootstrap, or anything else) reads CSS variables and data-* attributes. Sometic does not bundle Tailwind or Bootstrap.

When to use

• Runtime light / dark / system switching across Vanilla, React, Vue, or other adapters
• Token → CSS variable pipelines with a stable prefix
• Scoped themes on a subtree (not only :root)
• Density, RTL (dir), high-contrast, and reduced-motion flags as attributes
• Preference persistence across reloads via @sometic/store/persistent

When not to use

• Class / style / slot resolution only → @sometic/styling
• Compile-time Figma → code token CI → use Style Dictionary (or similar) and feed results into defineTokens
• A full visual CSS product as the deliverable → optional presets plus your own CSS
• Framework-only providers with no shared engine → keep those at the app boundary; this package stays framework-neutral

Package map

Surface	Import	Role
Theme controller	@sometic/theme	createThemeController, applyThemeToElement, snapshot types
Tokens	@sometic/theme/tokens	defineTokens, mergeTokens, resolveToken
CSS variables	@sometic/theme/css-variables	tokensToCssVariables, serializeCssVariables
Contrast	@sometic/theme/contrast	Hex parse, luminance, WCAG ratio helpers
System prefs	@sometic/theme/system	Color scheme, reduced motion, more contrast (lazy matchMedia)
Presets	@sometic/theme/presets	Minimal lightTheme / darkTheme for demos and tests

Presets stay on a subpath so apps that only need the controller do not pay for palettes. The controller root is about 4.4 KB gzip.

Architecture boundary

Package	Owns	Does not own
@sometic/theme	Tokens, generation, mode resolution, attributes, contrast helpers	Class merging, framework hooks
@sometic/styling	Classes, styles, slots, state attrs, resolveCssVariables	Design tokens
@sometic/store	Preference store, persistence adapters	Theme token math

Theme depends on styling’s resolveCssVariables and on store for subscriptions and optional persistence. Styling never owns tokens.

Quick start

import { createThemeController, applyThemeToElement } from "@sometic/theme";
import { lightTheme, darkTheme } from "@sometic/theme/presets";

const theme = createThemeController({
    themes: [lightTheme, darkTheme],
    defaultThemeId: lightTheme.id,
    lightThemeId: lightTheme.id,
    darkThemeId: darkTheme.id,
    mode: "system",
});

applyThemeToElement(document.documentElement, theme.get());

theme.subscribe((snapshot) => {
    applyThemeToElement(document.documentElement, snapshot);
});

theme.setMode("dark");

CSS then consumes variables such as var(--sometic-color-primary) and attributes such as [data-color-scheme="dark"].

Snapshot shape

Every get() / subscribe callback receives a ThemeSnapshot:

Field	Type (conceptually)	Meaning
preferences	ThemePreferences	Raw prefs: mode, themeId, density, direction, highContrast, reducedMotion
resolvedColorScheme	"light" | "dark"	Effective scheme after system resolution
resolvedThemeId	string	Theme actually used for tokens
tokens	ThemeTokens	Active token map
cssVariables	Record<string, string>	Flat --prefix-category-key map
attributes	Record<string, string>	data-theme, data-color-scheme, data-density, dir, optional contrast/motion flags

Docs in this section

Page	What you will learn
Installation	Install commands, peers, subpath imports
Tokens	defineTokens, merge, resolve paths
Themes	Register themes, mode vs theme id, presets
Runtime switching	Controller API, subscribe, dispose, scoped apply
CSS variables	Naming, serialize for SSR, apply cleanup
Tailwind	Map variables into Tailwind theme extensions
Bootstrap	Drive Bootstrap-styled UIs from variables and attrs
Plain CSS	Style with variables and state attributes only

Persistence

Pass persist: true with a storage adapter from @sometic/store/persistent. Defaults to in-memory storage unless you pass a web adapter, so durable browser prefs are explicit. Await hydrated before trusting restored values.

Deep dive: Theme store · Store

Contrast honesty

Contrast helpers parse hex colors (#rgb / #rrggbb) today. rgb(), hsl(), and OKLCH strings are not supported yet; invalid input fails closed (meetsWcagContrast → false, parseHexColor → undefined). Treat wider color spaces as a future extension, not current API.

Comparison (short)

Approach	Fit
Hand-written :root variables	Fine for static sites; Sometic adds registration, system mode, persistence, density/RTL, and a snapshot for any binding
next-themes / React-only providers	Great in Next.js; Sometic stays framework-neutral so Vanilla/Vue/Svelte share one engine
Style Dictionary	Compile-time pipelines; use both: generate at build time, switch at runtime with this package

Related

• Installation
• Tokens
• Themes
• Runtime switching
• CSS variables
• Theme store
• Store
• Styling guide