Anatomy of a Component

§1 - Tokens: the values every part reads

The theme is a set of CSS custom properties on :root (and the same keys with dark values on .dark), in the shape tweakcn exports. A component never names a colour, a radius or a shadow - it reads a token, so a theme swap or dark mode reaches every component at once. These are the tokens the Toggle reads:

:root {

  --accent:            oklch(0.9700 0 0);   /* pressed surface */

  --accent-foreground: oklch(0.2050 0 0);   /* pressed text */

  --muted:             oklch(0.9700 0 0);   /* hover surface */

  --muted-foreground:  oklch(0.5560 0 0);   /* resting text */

  --ring:              oklch(0.7080 0 0);   /* focus ring */

  --radius:            0.625rem;

  --radius-md:         calc(var(--radius) - 2px);

  --font-sans:         ui-sans-serif, system-ui, sans-serif;

}

.dark { /* the same keys, dark values */ }

§2 - Markup: one class, data attributes, native semantics

The HTML is a native element with one base class that says what it is. Variants and sizes are data-* attributes (the Data Attribute API), never modifier classes, and the state is a native or ARIA attribute - here aria-pressed, which is also what assistive technology reads.

<button class="toggle" aria-pressed="false" aria-label="Bold">

  <i data-lucide="bold"></i>

</button>

<button class="toggle" data-variant="outline" data-size="sm" aria-pressed="true">

  Italic

</button>

§3 - Stylesheet: the class reads the tokens

Every component stylesheet lives in @layer components and nests its variants, sizes and states under the base class. It reads tokens through var(--*) and derives hover colours with color-mix() - no hardcoded palette, so the same file renders every theme. The pressed look is the aria-pressed="true" attribute the markup already carries.

@layer components {

  .toggle {

    display: inline-flex;

    align-items: center;

    justify-content: center;

    gap: 0.5rem;

    font-size: 0.875rem;

    font-weight: 500;

    font-family: var(--font-sans);

    border-radius: var(--radius-md);

    border: 1px solid transparent;

    background: transparent;

    color: var(--muted-foreground);

    height: 2.25rem;

    padding: 0 0.5rem;

    &:hover:not(:disabled) { background-color: var(--muted); }

    &[aria-pressed="true"] {

      background-color: var(--accent);

      color: var(--accent-foreground);

      &:hover:not(:disabled) {

        background-color: color-mix(in oklch, var(--accent) 85%, var(--foreground));

      }

    }

    &:focus-visible { outline: 2px solid var(--ring); outline-offset: 2px; }

    &:disabled { opacity: 0.5; cursor: not-allowed; }

    &[data-variant="outline"] { /* ... */ }

    &[data-size="sm"] { /* ... */ }

  }

}

§4 - Script: only what HTML and CSS cannot do

Most components stop at the stylesheet. The Toggle needs one thing the platform does not give a button: flipping aria-pressed on click. Its module finds every .toggle through df$ (the core runtime: defuss-query for selection and events, defuss-morph for markup), guards against initializing twice, binds the State API so el.api.setState('pressed') and el.store work on every instance, and watches the document so elements added later initialize too. The attribute the script writes is the one the stylesheet reads - the script never styles anything.

function init() {

  dfDollar('.toggle:not([data-init]):not(.toggle-group .toggle)').each((_i, toggle) => {

    dfDollar(toggle).data('init', '');                 // the double-init guard

    toggle._defaultPressed = dfDollar(toggle).attr('aria-pressed') || 'false';

    // el.store + el.api: $('#my-toggle').api.setState('pressed')

    bindComponent(toggle, toggleApi, { name: toggle._defaultPressed === 'true' ? 'pressed' : 'default', config: {} });

    dfDollar(toggle).on('click', () => {

      dfDollar(toggle).attr('aria-pressed', String(dfDollar(toggle).attr('aria-pressed') !== 'true'));

    });

  });

}

init();

new MutationObserver(init).observe(document, { childList: true, subtree: true });

§5 - Component State API: named states in a store

Every component with a script exposes its states by name. Each element gets el.api.setState(name, config), el.api.getState() and el.api.render(state), and el.store: a defuss-store store of the state's name and config. The store follows every change, including the ones a user makes with a click, so a subscriber observes the component without polling; writing to the store applies the state as setState() does. A page or another component can therefore drive any component from outside and react to its changes through this API and the component's events, without knowing how it is built.

setState() applies a state to the live element through df$: attributes through defuss-query, markup through defuss-morph, which patches the existing DOM in place instead of replacing it. render(state) returns the element's markup in any state, as a string, built by the same function, so the UI that setState() produces and the markup render() describes cannot drift apart. The end-to-end test of every interactive component checks that they agree.

Some components add methods for interactions that a single state does not cover: df$.shadcn.toast.show() raises a toast, df$.shadcn.chart.deck() binds charts to a presentation, df$.shadcn.diagram.build() renders a diagram from JSON. Each component's page documents its whole API.

defuss-store is a micro-store for backing data that can also persist a store to localStorage or sessionStorage. Every component gets its store without extra code, and the shared layer's persisted() (df$.store for pages) adds the persistence: the big-data components keep their sort and filters this way by default, and these docs keep every remembered choice.

Every example on these pages runs in the HTML Preview Editor, so a component's behavior can be watched and tested where it is documented. Its State tab is generated from the component's schema and sets any state value directly; the example below binds the Toggle's.

§6 - Skill and schema: the component described

Two more files ship beside the stylesheet and the script. The component skill (component-skill.md) is the markup reference an agent reads before writing the HTML: the native basis, the structure, the variants, the ARIA and the states. The schema (toggle.schema.json) is the machine contract of the states: their names, types and defaults, how each is set and observed on the DOM - the docs' State tab is generated from it, and the verifier compares every page's States table against it.

§All six, live

The same markup three times under three token sets: the page's theme, a warm accent and the dark palette. Press any of them - the script flips the attribute, the stylesheet paints the state from whichever tokens are in scope.

§Where to go next

Configure variants and sizes in markup with the Data Attribute API, drive and observe the interactive components' named states through the State API, see how the stylesheets stack in Cascade Layers, and read a component's component skill before writing its HTML.

Comments, ideas or improvements? Edit this page's source on GitHub