hexo-theme-butterfly/layout/includes/head/darkmode.pug

script.
  var activateDarkMode = function () {
    document.documentElement.setAttribute('data-theme', 'dark')
    if (document.querySelector('meta[name="theme-color"]') !== null) {
      document.querySelector('meta[name="theme-color"]').setAttribute('content', '#000')
    }
  }
  var activateLightMode = function () {
    document.documentElement.setAttribute('data-theme', 'light')
    if (document.querySelector('meta[name="theme-color"]') !== null) {
      document.querySelector('meta[name="theme-color"]').setAttribute('content', '#fff')
    }
  }

  var getCookies = function (name) {
    const value = `; ${document.cookie}`
    const parts = value.split(`; ${name}=`)
    if (parts.length === 2) return parts.pop().split(';').shift()
  }

  var autoChangeMode = '#{theme.darkmode.autoChangeMode}'
  var t = getCookies('theme')
  if (autoChangeMode === '1') {
    var isDarkMode = window.matchMedia('(prefers-color-scheme: dark)').matches
    var isLightMode = window.matchMedia('(prefers-color-scheme: light)').matches
    var isNotSpecified = window.matchMedia('(prefers-color-scheme: no-preference)').matches
    var hasNoSupport = !isDarkMode && !isLightMode && !isNotSpecified

    if (t === undefined) {
      if (isLightMode) activateLightMode()
      else if (isDarkMode) activateDarkMode()
      else if (isNotSpecified || hasNoSupport) {
        console.log('You specified no preference for a color scheme or your browser does not support it. I Schedule dark mode during night time.')
        var now = new Date()
        var hour = now.getHours()
        var isNight = hour <= 6 || hour >= 18
        isNight ? activateDarkMode() : activateLightMode()
      }
      window.matchMedia('(prefers-color-scheme: dark)').addListener(function (e) {
        if (Cookies.get('theme') === undefined) {
          e.matches ? activateDarkMode() : activateLightMode()
        }
      })
    } else if (t === 'light') activateLightMode()
    else activateDarkMode()
  } else if (autoChangeMode === '2') {
    now = new Date()
    hour = now.getHours()
    isNight = hour <= 6 || hour >= 18
    if (t === undefined) isNight ? activateDarkMode() : activateLightMode()
    else if (t === 'light') activateLightMode()
    else activateDarkMode()
  } else {
    if (t === 'dark') activateDarkMode()
    else if (t === 'light') activateLightMode()
  }