# Fill Button

> A button that fills from the exact point your cursor enters and empties toward where it leaves, with a rolling label and a looping arrow.

Buttons · hover, button, fill, pointer · HTML, CSS, vanilla JS · no dependencies · updated 2026-10-16
Demo: https://kodza.dev/components/button-fill/

## Files

The code below, served as files: byte for byte what the Kodza site copies (the CSS includes its theme guard).

- [`kodza-button-fill.css`](https://kodza.dev/registry/button-fill/kodza-button-fill.css) · 7.8 KB
- [`kodza-button-fill.js`](https://kodza.dev/registry/button-fill/kodza-button-fill.js) · 4.0 KB
- [`kodza-button-fill.html`](https://kodza.dev/registry/button-fill/kodza-button-fill.html) · 0.6 KB · the markup, to adapt and paste into your page

**Can you run shell commands? Download the CSS and the JS, don't retype them.** Retyping costs thousands of tokens and can drop or change lines of the CSS. Put the files where your stack expects them (Use it says where: change the `-o` paths):

```bash
curl -fsSL --create-dirs -o kodza/kodza-button-fill.css https://kodza.dev/registry/button-fill/kodza-button-fill.css
curl -fsSL --create-dirs -o kodza/kodza-button-fill.js https://kodza.dev/registry/button-fill/kodza-button-fill.js
```

Then load the files from your page as Use it shows, instead of pasting the content. The HTML is the part you adapt (text, links, modifiers): paste it from the Code section. Copy the CSS and the JS from the Code section only if you can't run commands, exactly as they are. (Windows PowerShell: `curl.exe`.)

## API

- Root: `.kodza-fill-button`
- Element: an `<a href>` for a link, or a `<button type="button">` (`type="submit"` in a form) for an action. Same classes, same look.
- Variables (set them on the root element itself: it declares its own defaults):
  - `--kz-fill-fg: #0a0a0a`
  - `--kz-fill-bg: transparent`
  - `--kz-fill-border: rgba(10, 10, 10, 0.9)`
  - `--kz-fill-fill: #0a0a0a`
  - `--kz-fill-fill-fg: #ffffff`
  - `--kz-fill-radius: 999px`
  - `--kz-fill-height: 52px`
  - `--kz-fill-pad-x: 28px`
  - `--kz-fill-gap: 10px`
  - `--kz-fill-duration: 0.65s`
  - `--kz-fill-ease: cubic-bezier(0.22, 1, 0.36, 1)`
- Modifiers: `.kodza-fill-button--solid`
- Lifecycle: `kodza:init` / `kodza:destroy` on `document`, with `{ detail: { root } }` to target a container.

## Dark mode

The values Kodza uses on a dark background (`#0a0a0a`). For a page that follows the system theme, add them after the component's CSS:

```css
@media (prefers-color-scheme: dark) {
  .kodza-fill-button {
    --kz-fill-fg: #ffffff;
    --kz-fill-border: rgba(255, 255, 255, 0.85);
    --kz-fill-fill: #ffffff;
    --kz-fill-fill-fg: #0a0a0a;
  }

  .kodza-fill-button--solid {
    --kz-fill-bg: #ffffff;
    --kz-fill-fg: #0a0a0a;
    --kz-fill-border: transparent;
    --kz-fill-fill: #d9d9d5;
    --kz-fill-fill-fg: #0a0a0a;
  }
}
```

A site with its own theme switch puts the same rules under its dark selector instead (`[data-theme="dark"] .kodza-fill-button { … }`); a single dark section, under that section's class.

## Use it

### Plain HTML page

- CSS: `kodza/kodza-button-fill.css` next to the page (the Files commands as they are), linked in `<head>`: `<link rel="stylesheet" href="kodza/kodza-button-fill.css">`. Without a shell, paste it in a `<style>` in `<head>` instead. It only touches `kodza-` classes.
- HTML: where the component goes. Paste it as many times as you need: instances never interfere.
- JS: `kodza/kodza-button-fill.js`, loaded with `<script src="kodza/kodza-button-fill.js" defer></script>` in `<head>`. Without a shell, paste it in a `<script>` before `</body>` (or in `<head>`: it waits for the page). One copy per page, whatever the number of instances.
- Restyle with the `--kz-…` variables, set on the component's root element itself (the root declares its own defaults, so a value on an ancestor is ignored), and with the modifiers / attributes listed under API.
- Font: it takes the page's own. The Kodza look is Geist: `<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Geist:wght@400;500;600;700&family=Geist+Mono:wght@400;500&display=swap">`.
- Content added later (AJAX navigation, a SPA route, a builder preview): start it with `document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: container } }))`; before removing it, the same call with `'kodza:destroy'` stops it and puts the original markup back.

### Claude artifact (claude.ai)

- Paste the CSS in a `<style>` and the JS in a `<script>` at the end, in the artifact itself: it loads stylesheets only from Google Fonts and scripts only from a few CDNs, so no `<link>` or `<script src>` to Kodza.
- Writing the artifact file with a shell? Insert the downloaded files (Files) with a command instead of retyping them: a line `KODZA-CSS` alone inside the `<style>`, `KODZA-JS` inside the `<script>`, then `sed -e '/^KODZA-CSS$/{r kodza/kodza-button-fill.css' -e 'd' -e '}' -e '/^KODZA-JS$/{r kodza/kodza-button-fill.js' -e 'd' -e '}' page.html > artifact.html`.
- Font: load Geist from Google Fonts (allowed): `<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Geist:wght@400;500;600;700&family=Geist+Mono:wght@400;500&display=swap">`.
- Dark mode: the viewer sets `data-theme="dark"` or `"light"` on `<html>`, or nothing when it follows the system. Write the Dark mode rules twice: inside `@media (prefers-color-scheme: dark)` with `:root:not([data-theme="light"])` in front of each selector, and with `:root[data-theme="dark"]` in front of each selector.

### WordPress

- HTML: a **Custom HTML** block (or a pattern / template part). WordPress keeps this markup as it is only for users allowed to post unfiltered HTML (Administrators; Super Admins on multisite): for anyone else it strips tags such as `<svg>`, `<input>` or `<dialog>`, so add it from the theme (a pattern or template part) instead.
- This one is inline (it flows like a word): pasted alone, many themes leave it at the edge of the page (block themes, and classic ones like Twenty Twenty-One or Blocksy), so put the Custom HTML block inside a **Group** block to line it up with the text.
- CSS and JS: the downloaded files go in the theme, under `wp-content/themes/<your-theme>/kodza/` (the child theme if there is one), enqueued from its functions.php (or a code-snippets plugin):
  ```php
  add_action('wp_enqueue_scripts', function () {
    $dir = get_stylesheet_directory() . '/kodza/';
    $uri = get_stylesheet_directory_uri() . '/kodza/';
    wp_enqueue_style('kodza-button-fill', $uri . 'kodza-button-fill.css', [], filemtime($dir . 'kodza-button-fill.css'));
    wp_enqueue_script('kodza-button-fill', $uri . 'kodza-button-fill.js', [], filemtime($dir . 'kodza-button-fill.js'), true);
  });
  ```
  Scoped to `kodza-` classes, the CSS never touches the theme. One copy of the JS, whatever the number of blocks.
- No access to the theme files? The CSS can also go, as it is, in **Appearance → Customize → Additional CSS** (classic theme) or **Styles → Additional CSS** in the Site Editor (block theme).
- Theme with AJAX page transitions: fire `kodza:init` on the new content after each swap (and `kodza:destroy` on the old one).
- Performance plugin (WP Rocket, LiteSpeed Cache, Perfmatters…) with **Delay JavaScript execution** turned on: add `kodza` to the scripts it must not delay. Otherwise the component waits for the visitor's first scroll, tap or mouse move, and that first click can be lost.
- Colours: by default, match the theme's palette. After the component's CSS, point these variables at the theme's colours, on the component root, Kodza's value as the fallback:
  `.kodza-fill-button { --kz-fill-fg: var(TEXT, #0a0a0a); --kz-fill-fill: var(ACCENT, #0a0a0a); --kz-fill-fill-fg: var(BACKGROUND, #ffffff); }`
  `.kodza-fill-button--solid { --kz-fill-bg: var(ACCENT, #0a0a0a); --kz-fill-fg: var(BACKGROUND, #ffffff); --kz-fill-fill: #e9e9e6; --kz-fill-fill-fg: #0a0a0a; }`
  (the line after the first: a variant that sets its own colours; without it, the first line would override it)
  TEXT, BACKGROUND and ACCENT (the colour the theme fills its own buttons with) are the theme's own colour variables — block themes (theme.json, like Twenty Twenty-Five): `--wp--preset--color--contrast`, `--wp--preset--color--base`, `--wp--preset--color--contrast` (they fill their buttons with it; their accent-1… colours are decorative); Astra: `--ast-global-color-2`, `--ast-global-color-4`, `--ast-global-color-0`; Kadence: `--global-palette3`, `--global-palette9`, `--global-palette1`; GeneratePress: `--contrast`, `--base-3`, `--accent`; Blocksy: `--theme-palette-color-4`, `--theme-palette-color-8`, `--theme-palette-color-1`. Use only these names, and only if the site really has them (the theme's CSS, or Styles → Colors): the `--wp--preset--color--black`, `--white`, `--vivid-…` that WordPress adds everywhere are not the theme's palette. Another theme, or one without these variables (Hello Elementor, OceanWP): leave the variables alone, it keeps Kodza's monochrome; same when the developer asks for monochrome or the Kodza look. Leave the translucent greys (`rgba(10, 10, 10, …)`) as they are: they suit any light background. On a dark palette, set the other variables from Dark mode too.
- WordPress turns straight quotes and `--` into typographic ones in the text of a Custom HTML block (not inside `<code>` or `<pre>`).

#### With Elementor

- HTML: an **HTML** widget (Elementor shows it to administrators only). It keeps the code exactly as pasted, straight quotes included.
- CSS and JS: as above. Elementor's Site Settings → Theme Style styles every button, field, link and image of the page, components included; the theme guard at the end of the CSS keeps the component's buttons, fields and link colours as they are.
- The Elementor editor redraws each widget after the page has loaded: without the script below, the component stays still in the editor preview (the published page works). Add it once per site, in the footer like the component's script (`kodza/elementor-editor.js`, or a code-snippets plugin):

```js
// Kodza in the Elementor editor: the editor redraws each HTML widget after the page has loaded.
// Start Kodza in what it draws, stop it in what it replaces or removes. Once per site.
window.addEventListener('elementor/frontend/init', () => {
  if (!elementorFrontend.isEditMode()) return;
  class KodzaWidget extends elementorModules.frontend.handlers.Base {
    onInit() {
      super.onInit();
      this.kodza = [...this.$element[0].children];
      document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: this.$element[0] } }));
    }
    onDestroy() {
      super.onDestroy();
      this.kodza.forEach((root) => document.dispatchEvent(new CustomEvent('kodza:destroy', { detail: { root } })));
    }
  }
  elementorFrontend.elementsHandler.attachHandler('html', KodzaWidget);
});
```

- No child theme: everything can go in the HTML widget instead, `<style>` with the CSS, the HTML, then `<script>` with the JS. It works on the page and in the editor without the script above.

### Shopify

- Files: `assets/kodza-button-fill.css` and `assets/kodza-button-fill.js` (the Files commands with `-o assets/…`).
- In the section: `{{ 'kodza-button-fill.css' | asset_url | stylesheet_tag }}` and `<script src="{{ 'kodza-button-fill.js' | asset_url }}" defer></script>`, then the HTML.
- The theme editor re-renders sections: restart them with
  `document.addEventListener('shopify:section:load', (e) => document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root: e.target } })));`
  and the same with `shopify:section:unload` → `kodza:destroy`.

### React / Next.js

- Files, side by side (e.g. in `components/kodza/`): `FillButton.tsx` (below), the CSS block under Code saved as `button-fill.css` and the JS block as `button-fill.js`, both as they are. The HTML block is already inside the component: skip it.
- Use it: `import { FillButton } from '@/components/kodza/FillButton';` then `<FillButton>Copy. Paste. Ship.</FillButton>`. Props: `variant` ("solid", or several in an array), `vars` (the `--kz-…` variables listed under API, e.g. `vars={{ '--kz-fill-fg': … }}`), `children` (the text, plain), `className`, `style` and the other props of its `<a>` (`onClick`, `aria-…`).
- Next.js App Router: it is a Client Component already (`'use client'`). Pages Router: Next.js takes global CSS only in `pages/_app`, so move the `import './button-fill.css'` line there.
- Safe under StrictMode, client-side navigation and prop changes: when a prop changes, the `key` gives React a fresh element, `kodza:destroy` stops the script on the old one and `kodza:init` starts it on the new one.

```tsx
'use client';
// Kodza — Fill Button, for React. From https://kodza.dev/components/button-fill/
// Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license
// Next to this file: button-fill.css and button-fill.js, the component's CSS and JS from Kodza, as they are.
// Yours to edit: the markup is plain JSX below.
// The script changes this markup once React has rendered it (it adds layers, splits text, moves
// nodes), so React must not patch it afterwards. When a prop changes, the key gives React a fresh
// element: kodza:destroy stops the script on the old one, kodza:init starts it on the new one.
import { useRef, useEffect, type ComponentPropsWithoutRef, type ComponentRef, type CSSProperties } from 'react';
import './button-fill.css';

type Variant = "solid";

export type FillButtonProps = Omit<ComponentPropsWithoutRef<'a'>, "children" | "variant" | "vars"> & {
  /** Modifier class(es): .kodza-fill-button--solid */
  variant?: Variant | Variant[];
  /** Settings, as CSS variables on the root */
  vars?: {
    /** default: #0a0a0a */
    "--kz-fill-fg"?: string | number;
    /** default: transparent */
    "--kz-fill-bg"?: string | number;
    /** default: rgba(10, 10, 10, 0.9) */
    "--kz-fill-border"?: string | number;
    /** default: #0a0a0a */
    "--kz-fill-fill"?: string | number;
    /** default: #ffffff */
    "--kz-fill-fill-fg"?: string | number;
    /** default: 999px */
    "--kz-fill-radius"?: string | number;
    /** default: 52px */
    "--kz-fill-height"?: string | number;
    /** default: 28px */
    "--kz-fill-pad-x"?: string | number;
    /** default: 10px */
    "--kz-fill-gap"?: string | number;
    /** default: 0.65s */
    "--kz-fill-duration"?: string | number;
    /** default: cubic-bezier(0.22, 1, 0.36, 1) */
    "--kz-fill-ease"?: string | number;
  };
  /** The text, plain: the script reads it and rebuilds the markup around it */
  children?: string;
  className?: string;
};

export function FillButton({ variant, vars, children = "Copy. Paste. Ship.", className, style, ...rest }: FillButtonProps) {
  const ref = useRef<ComponentRef<'a'>>(null);
  const classes = ["kodza-fill-button", ...([] as string[]).concat(variant ?? []).map((v) => `kodza-fill-button--${v}`), className].filter(Boolean).join(' ');
  // Everything the markup is made of: when it changes, React gets a fresh element (see the top)
  const key = JSON.stringify([classes, vars, children, style, rest]);

  // Starts the script on this element once React has rendered it, stops it when it goes
  useEffect(() => {
    const root = ref.current;
    let live = true;
    // @ts-ignore: a plain script, no types to find
    import('./button-fill.js').then(() => {
      if (live) document.dispatchEvent(new CustomEvent('kodza:init', { detail: { root } }));
    });
    return () => {
      live = false;
      document.dispatchEvent(new CustomEvent('kodza:destroy', { detail: { root } }));
    };
  }, [key]);

  return (
    <a href="#" key={key} {...rest} className={classes} style={{ ...vars, ...style } as CSSProperties} ref={ref}>
      <span className="kodza-fill-button__label">{children}</span>
    </a>
  );
}
```

## Code

```html
<a class="kodza-fill-button" href="#">
  <span class="kodza-fill-button__label">Copy. Paste. Ship.</span>
</a>

<a class="kodza-fill-button kodza-fill-button--solid" href="#">
  <span class="kodza-fill-button__label">Get Kodza</span>
</a>

<a class="kodza-fill-button" href="#">
  <span class="kodza-fill-button__label">Skip the setup</span>
  <span class="kodza-fill-button__icon" aria-hidden="true">
    <svg viewBox="0 0 16 16"><path d="M3 8h10M9 4l4 4-4 4" fill="none" stroke="currentColor" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round" /></svg>
  </span>
</a>
```

```css
/* Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license */
/* Kodza — Fill Button
   The fill grows from the exact point the pointer enters, and leaves where it exits.
   Everything is tuned with the --kz-fill-* variables. */
.kodza-fill-button {
  --kz-fill-fg: #0a0a0a;
  --kz-fill-bg: transparent;
  --kz-fill-border: rgba(10, 10, 10, 0.9);
  --kz-fill-fill: #0a0a0a;
  --kz-fill-fill-fg: #ffffff;
  --kz-fill-radius: 999px;
  --kz-fill-height: 52px;
  --kz-fill-pad-x: 28px;
  --kz-fill-gap: 10px;
  --kz-fill-duration: 0.65s;
  --kz-fill-ease: cubic-bezier(0.22, 1, 0.36, 1);

  position: relative;
  display: inline-grid;
  height: var(--kz-fill-height);
  padding: 0;
  border: 0;
  border-radius: var(--kz-fill-radius);
  background: var(--kz-fill-bg);
  box-shadow: inset 0 0 0 1.5px var(--kz-fill-border);
  color: var(--kz-fill-fg);
  font: inherit;
  font-weight: 500;
  letter-spacing: -0.01em;
  text-decoration: none;
  white-space: nowrap;
  cursor: pointer;
  overflow: hidden;
  isolation: isolate;
  -webkit-tap-highlight-color: transparent;
  transition: transform 0.25s var(--kz-fill-ease);
}

.kodza-fill-button:active {
  transform: scale(0.97);
}

.kodza-fill-button:focus-visible {
  outline: 2px solid var(--kz-fill-fill);
  outline-offset: 3px;
}

/* The content exists twice: underneath (resting colors) and inside the fill
   (inverted colors). The circle reveals the second copy, so the text changes
   color exactly under the edge of the circle. */
.kodza-fill-button__content,
.kodza-fill-button__fill {
  grid-area: 1 / 1;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: var(--kz-fill-gap);
  padding: 0 var(--kz-fill-pad-x);
}

.kodza-fill-button__fill {
  background: var(--kz-fill-fill);
  color: var(--kz-fill-fill-fg);
  clip-path: circle(0% at var(--kz-x, 50%) var(--kz-y, 50%));
  transition: clip-path var(--kz-fill-duration) var(--kz-fill-ease);
  pointer-events: none;
}

.kodza-fill-button.is-hover .kodza-fill-button__fill,
.kodza-fill-button:focus-visible .kodza-fill-button__fill {
  clip-path: circle(150% at var(--kz-x, 50%) var(--kz-y, 50%));
}

/* Rolling label: the line leaves through the top, its copy comes in from below */
.kodza-fill-button__label {
  position: relative;
  display: block;
  overflow: hidden;
  line-height: 1.25;
}

.kodza-fill-button__label > span {
  display: block;
  transition: transform var(--kz-fill-duration) var(--kz-fill-ease);
}

.kodza-fill-button__label > span::after {
  content: attr(data-text);
  position: absolute;
  top: 100%;
  left: 0;
}

.kodza-fill-button.is-hover .kodza-fill-button__label > span,
.kodza-fill-button:focus-visible .kodza-fill-button__label > span {
  transform: translateY(-100%);
}

/* Optional arrow: it leaves on the right and comes back from the left */
.kodza-fill-button__icon {
  position: relative;
  display: block;
  width: 1em;
  height: 1em;
  overflow: hidden;
}

.kodza-fill-button__icon svg {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  transition: transform var(--kz-fill-duration) var(--kz-fill-ease);
}

.kodza-fill-button__icon svg + svg {
  transform: translateX(-110%);
}

.kodza-fill-button.is-hover .kodza-fill-button__icon svg,
.kodza-fill-button:focus-visible .kodza-fill-button__icon svg {
  transform: translateX(110%);
}

.kodza-fill-button.is-hover .kodza-fill-button__icon svg + svg,
.kodza-fill-button:focus-visible .kodza-fill-button__icon svg + svg {
  transform: translateX(0);
}

/* Solid variant: the button starts filled, the circle brings the accent color */
.kodza-fill-button--solid {
  --kz-fill-bg: #0a0a0a;
  --kz-fill-fg: #ffffff;
  --kz-fill-border: transparent;
  --kz-fill-fill: #e9e9e6;
  --kz-fill-fill-fg: #0a0a0a;
}

/* Without JavaScript: the button simply swaps colors on hover */
.kodza-fill-button:not(.is-ready):hover {
  background: var(--kz-fill-fill);
  color: var(--kz-fill-fill-fg);
}

@media (prefers-reduced-motion: reduce) {
  .kodza-fill-button,
  .kodza-fill-button__fill,
  .kodza-fill-button__label > span,
  .kodza-fill-button__icon svg {
    transition-duration: 0.01ms;
  }
}

/* Theming example — on a dark background:
.dark-section .kodza-fill-button {
  --kz-fill-fg: #ffffff;
  --kz-fill-border: rgba(255, 255, 255, 0.85);
  --kz-fill-fill: #ffffff;
  --kz-fill-fill-fg: #0a0a0a;
}
*/

/* kodza-guard d60305b52cb0 — generated by Kodza, do not edit.
   Theme guard: keeps a site's own CSS (WordPress themes, Bootstrap, CSS resets…) off this
   component. :not(#_) is always true and weighs as much as an id, so these lines win over
   theme rules made of classes and tags. Customise the component through its --kz-* variables. */

/* What the browser gives, where the component sets it only in some states: at the lowest weight, so its own rules below put it back */

:where(.kodza-fill-button):not(#_) {
  outline: revert;
  outline-offset: revert;
}

/* What the browser gives, on everything the component leaves to it */

.kodza-fill-button:not(#_) {
  list-style: revert;
  box-sizing: revert;
  appearance: revert;
  max-height: revert;
  text-transform: revert;
  text-underline-offset: revert;
  text-align: revert;
  text-indent: revert;
  text-shadow: revert;
  vertical-align: revert;
  min-height: revert;
}

.kodza-fill-button__content:not(#_),
.kodza-fill-button__label:not(#_),
.kodza-fill-button__fill:not(#_),
.kodza-fill-button__icon:not(#_),
.kodza-fill-button__label span:where(:not([class*="kodza-"])):not(#_) {
  box-sizing: revert;
}

.kodza-fill-button__icon svg:where(:not([class*="kodza-"])):not(#_) {
  border: revert;
  margin: revert;
  padding: revert;
  border-radius: revert;
  outline: revert;
  text-decoration: revert;
  list-style: revert;
  box-sizing: revert;
  float: revert;
  background-color: revert;
  background-image: revert;
  box-shadow: revert;
  outline-offset: revert;
  appearance: revert;
  max-width: revert;
  max-height: revert;
  color: revert;
  font-family: revert;
  font-size: revert;
  font-weight: revert;
  font-style: revert;
  line-height: revert;
  letter-spacing: revert;
  text-transform: revert;
  text-underline-offset: revert;
  text-align: revert;
  text-indent: revert;
  text-shadow: revert;
  vertical-align: revert;
}

.kodza-fill-button__icon svg:where(:not([class*="kodza-"])):not(#_):where(:not([hidden])) {
  display: revert;
}

.kodza-fill-button__icon svg:where(:not([class*="kodza-"])):not(#_):where([hidden]) {
  display: none;
}

/* The component's own rules, one step stronger: real buttons and fields, what it sets on tags themes style (links, lists, headings, images…), and the root width (a theme may narrow it, never widen it) */

.kodza-fill-button:not(#_) {
  position: relative;
  display: inline-grid;
  height: var(--kz-fill-height);
  padding: 0;
  border: 0;
  border-radius: var(--kz-fill-radius);
  background: var(--kz-fill-bg);
  box-shadow: inset 0 0 0 1.5px var(--kz-fill-border);
  color: var(--kz-fill-fg);
  font: inherit;
  font-weight: 500;
  letter-spacing: -0.01em;
  text-decoration: none;
  white-space: nowrap;
  cursor: pointer;
  overflow: hidden;
  isolation: isolate;
  -webkit-tap-highlight-color: transparent;
  transition: transform 0.25s var(--kz-fill-ease);
}

.kodza-fill-button:active:not(#_) {
  transform: scale(0.97);
}

.kodza-fill-button:focus-visible:not(#_) {
  outline: 2px solid var(--kz-fill-fill);
  outline-offset: 3px;
}

.kodza-fill-button__icon svg:not(#_) {
  position: absolute;
  transition: transform var(--kz-fill-duration) var(--kz-fill-ease);
}

.kodza-fill-button:not(.is-ready):hover:not(#_) {
  background: var(--kz-fill-fill);
  color: var(--kz-fill-fill-fg);
}

@media (prefers-reduced-motion: reduce) {
  .kodza-fill-button:not(#_) {
    transition-duration: 0.01ms;
  }
}

@media (prefers-reduced-motion: reduce) {
  .kodza-fill-button__icon svg:not(#_) {
    transition-duration: 0.01ms;
  }
}
```

```js
// Kodza License: free to use, client work included. Not to resell or redistribute, ported or not: https://kodza.dev/docs/#print-license
// Kodza — Fill Button
// Prepares every .kodza-fill-button (a copy of its content for the fill, a rolling label)
// and follows where the pointer enters and leaves.
(() => {
  const SELECTOR = '.kodza-fill-button';

  // One instance. Everything it starts is tied to `signal`, so kodza:destroy stops it all
  function mount(button, signal) {
    // 1. The original content moves into a resting layer
    const content = document.createElement('span');
    content.className = 'kodza-fill-button__content';
    content.append(...button.childNodes);
    button.append(content);

    // 2. Each label gets a copy of itself for the roll
    content.querySelectorAll('.kodza-fill-button__label').forEach((label) => {
      const text = label.textContent.trim();
      label.innerHTML = '';
      const line = document.createElement('span');
      line.dataset.text = text;
      line.textContent = text;
      label.append(line);
    });

    // 3. The arrow, if any, is doubled so it can loop
    content.querySelectorAll('.kodza-fill-button__icon').forEach((icon) => {
      const svg = icon.querySelector('svg');
      if (svg) icon.append(svg.cloneNode(true));
    });

    // 4. The filled layer is a copy, hidden from screen readers
    const fill = content.cloneNode(true);
    fill.className = 'kodza-fill-button__fill';
    fill.setAttribute('aria-hidden', 'true');
    button.append(fill);

    // 5. The circle grows from the entry point and closes toward the exit point
    const track = (event) => {
      const rect = button.getBoundingClientRect();
      button.style.setProperty('--kz-x', `${((event.clientX - rect.left) / rect.width) * 100}%`);
      button.style.setProperty('--kz-y', `${((event.clientY - rect.top) / rect.height) * 100}%`);
    };
    button.addEventListener('pointerenter', (event) => {
      track(event);
      button.classList.add('is-hover');
    }, { signal });
    button.addEventListener('pointerleave', (event) => {
      track(event);
      button.classList.remove('is-hover');
    }, { signal });
    // With the keyboard, the fill starts from the center
    button.addEventListener('focus', () => {
      if (!button.matches(':hover')) {
        button.style.setProperty('--kz-x', '50%');
        button.style.setProperty('--kz-y', '50%');
      }
    }, { signal });
  }

  // Kodza lifecycle, the same in every component: `kodza:init` starts the instances inside
  // event.detail.root (the whole page by default), `kodza:destroy` stops them and puts their
  // markup back. For themes and apps that swap content without a page load.
  const instances = new WeakMap();
  const find = (scope = document) => [scope, ...scope.querySelectorAll(SELECTOR)].filter((el) => el.matches?.(SELECTOR));
  const init = (scope) => find(scope).forEach((root) => {
    if (root.classList.contains('is-ready')) return; // already running, maybe from another copy of this script
    const controller = new AbortController();
    instances.set(root, { controller, html: root.innerHTML, attrs: [...root.attributes].map((a) => [a.name, a.value]) });
    mount(root, controller.signal);
    root.classList.add('is-ready');
  });
  const destroy = (scope) => find(scope).forEach((root) => {
    const instance = instances.get(root);
    if (!instance) return;
    instances.delete(root);
    instance.controller.abort();
    [...root.attributes].forEach((a) => root.removeAttribute(a.name));
    instance.attrs.forEach(([name, value]) => root.setAttribute(name, value));
    root.innerHTML = instance.html;
  });
  document.addEventListener('kodza:init', (event) => init(event.detail?.root));
  document.addEventListener('kodza:destroy', (event) => destroy(event.detail?.root));
  init();
  // Loaded in <head>, the script runs before the markup exists: once more when it is parsed
  if (document.readyState === 'loading') document.addEventListener('DOMContentLoaded', () => init(), { once: true });
})();
```

Free to use, from Kodza (https://kodza.dev).