navidrome/ui/src/themes/useCurrentTheme.js

import { useSelector } from 'react-redux'
import useMediaQuery from '@material-ui/core/useMediaQuery'
import themes from './index'
import { AUTO_THEME_ID } from '../consts'
import config from '../config'

export default () => {
  const prefersLightMode = useMediaQuery('(prefers-color-scheme: light)')
  return useSelector((state) => {
    if (state.theme === AUTO_THEME_ID) {
      return prefersLightMode ? themes.LightTheme : themes.DarkTheme
    }
    const themeName =
      state.theme ||
      Object.keys(themes).find(
        (t) => themes[t].themeName === config.defaultTheme
      ) ||
      'DarkTheme'
    return themes[themeName]
  })
}