React Theme Switch Using CSS

index.tsx

import * as React from 'react';
import ReactDOM from 'react-dom';
import './theme.css'

export enum Icon {
  DARK = '🌘',
  LIGHT = '🌦'
}

export enum Theme {
  DARK = "dark",
  LIGHT = "light",
}

const updateFavicon = (updated: string) => {
  const favicon = document.querySelector<HTMLLinkElement>("#favicon");
  return favicon ? favicon.href = `/path/to/assets/${updated}.svg` : '';
}

const Toggle = (props: any) => {
  
  const [theme, setTheme] = React.useState<string>(Theme.DARK);
  const nextTheme = theme === Theme.LIGHT ? Theme.DARK : Theme.LIGHT;

  
  React.useEffect(() => {
    document.body.dataset.theme = theme;
    updateFavicon(Theme.DARK);
  }, [theme]);

  const updateTheme = () => {
    setTheme(nextTheme)
    updateFavicon(Theme.DARK)
  }
  
  return (
    <button onClick={updateTheme}>
      <>{theme === 'dark' ? Icon.DARK : Icon.LIGHT}</>
    </button>
  )
}

const App = () => <><Toggle/></>;

ReactDOM.render(
  <React.StrictMode>
    <App />
  </React.StrictMode>,
  document.getElementById('root')
);

theme.css

body[data-theme="dark"] {
  --bg: hsl(220deg 26% 14%);
  --pColor: hsl(214deg 20% 69%);
  --h1Color: hsl(0deg 0% 99%);
  --aColor: hsl(214deg 20% 69%);
  --aHoverColor: hsl(0deg 0% 99%);
  --inputColor: hsl(0deg 0% 99%);
}

body[data-theme="light"] {
  --bg: hsl(0deg 0% 99%);
  --pColor: hsl(220deg 27% 28%);
  --h1Color: hsl(220deg 26% 14%);
  --aColor: hsl(220deg 27% 28%);
  --aHoverColor: hsl(220deg 26% 14%);
  --inputColor: hsl(0deg 0% 0% / 10%);
}

body {
  font-family: proxima-nova, sans-serif;
  display: flex;
  justify-content: center;
  background: var(--bg);
  color: var(--text-color);
  margin: 0;
  padding: 0;
}
/* Remove ugly scrollbar on desktop */
body::-webkit-scrollbar {
  width: 0.25rem;
}

body::-webkit-scrollbar-track {
  background: rgb(9, 31, 45);
}

body::-webkit-scrollbar-thumb {
  background: #000000;
}