
Use the `useRootStyles` [flag](/docs/theming/theme#configuration-flags) and `styles.root` key in your theme to set theme-aware styles for any elements.

```js title=theme.js
const theme = {
  useRootStyles: true, // highlight-line
  styles: {
    // Applies to <html />.
    root: {
      m: 0,
      p: 0,

      "*": {
        boxSizing: "border-box",
      },

      // Applies to <body />
      body: {
        fontSize: "sm",
      },
    },
  },
}
```

<Callout>

`useRootStyles: true` applies `styles.root` to `html`.

`useRootStyles: false` applies `styles.root` to `body`.

</Callout>


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