lightning-address/pages/_app.js

import { createGlobalStyle, ThemeProvider } from 'styled-components'

const GlobalStyle = createGlobalStyle`
  @import url('https://fonts.googleapis.com/css2?family=Inter:wght@200;400;700;900&display=swap');

  body {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Inter', sans-serif;
  }

  ::selection {
    background-color: rgba(0,118,255,0.9);
    color: #fff;
  }
`

const theme = {
  colors: {
    primary: 'rgba(0,118,255,0.9)',
  },
}

export default function App({ Component, pageProps }) {
  return (
    <>
      <GlobalStyle />
      <ThemeProvider theme={theme}>
        <Component {...pageProps} />
      </ThemeProvider>
    </>
  )
}