> ## Documentation Index > Fetch the complete documentation index at: https://docs.vertz.dev/llms.txt > Use this file to discover all available pages before exploring further. # Mount > API reference for mount() — rendering your app to the DOM `mount()` renders your app component into the `#app` root element. It handles both fresh rendering and hydration of server-rendered HTML. ## Signature ```ts theme={null} import { mount } from '@vertz/ui'; mount(App, options?); ``` ### Parameters | Parameter | Type | Description | | --------- | ----------------------------------- | ------------------------------------------------------ | | `app` | `() => Element \| DocumentFragment` | Component function that returns the app's root element | | `options` | `MountOptions` | Optional configuration | ### MountOptions | Option | Type | Description | | --------- | ----------------------------- | ----------------------------------------------------------------- | | `theme` | `Theme` | Design tokens from `defineTheme()` — compiled to CSS and injected | | `styles` | `string[]` | Global CSS strings to inject into `` | | `onMount` | `(root: HTMLElement) => void` | Callback fired after mount completes | ### Returns `MountHandle` — an object with a `dispose()` method to unmount the app. ## Usage ### Basic ```ts theme={null} import { mount } from '@vertz/ui'; import { App } from './app'; mount(App); ``` ### With theme and styles ```ts theme={null} import { mount } from '@vertz/ui'; import { App, styles } from './app'; import { appTheme } from './styles/theme'; mount(App, { theme: appTheme, styles, }); ``` ## Root element `mount()` always targets `#app` — there is no selector parameter. The framework controls the HTML in every context (SSR, dev server, scaffolded templates), so the root element is always `
`. If `#app` is not found in the document, `mount()` throws an error. ## Hydration When server-rendered HTML exists inside `#app`, `mount()` performs tolerant hydration — it walks the existing DOM and adopts server-rendered nodes instead of replacing them. If hydration fails (mismatched structure), it falls back to full client-side rendering automatically.