Import ThemeProvider at the top of your React component tree

App.js

import * as React from 'react';
import Constants from 'expo-constants';
import { ThemeProvider } from '@shopify/restyle';

// You can import from local files
import theme from './theme';
import AssetExample from './components/AssetExample';
import Box from './components/Box';
import Text from './components/Text';

export default function App() {
  return (
    <ThemeProvider theme={theme}>
      <Box
        flex={1}
        justifyContent="center"
        backgroundColor="mainBackground"
        padding="s">
        <Text variant="header" textAlign="center">
          Hello world
        </Text>
        <Text variant="paragraph">
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        </Text>
        <AssetExample />
      </Box>
    </ThemeProvider>
  );
}