refact: rework theme code

fix: lint errors

fix: lint error

fix: lint error

gatsby-ssr.js

@@ -1,31 +1,7 @@
-import React from "react"
+/**
+ * Implement Gatsby's SSR (Server Side Rendering) APIs in this file.
+ *
+ * See: https://www.gatsbyjs.org/docs/ssr-apis/
+ */
 
-const ThemeScript = () => {
-  const themeScript = `
-(function() {
-  function getInitialTheme() {
-    const userSetTheme = window.localStorage.getItem("theme")
-    const prefersLightTheme = window.matchMedia(
-      "(prefers-color-scheme: light)"
-    )
-
-    if (userSetTheme && userSetTheme !== '"unset"') return userSetTheme
-    else if (prefersLightTheme.matches === true) return "light"
-    else return "dark"
-  }
-
-  if (typeof document === "undefined") return;
-
-  document.documentElement.style.setProperty(
-    "--initial-theme",
-    getInitialTheme()
-  )
-})()
-  `
-
-  return <script dangerouslySetInnerHTML={{ __html: themeScript }} />
-}
-
-export const onRenderBody = ({ setPreBodyComponents }) => {
-  setPreBodyComponents(<ThemeScript></ThemeScript>)
-}
+// You can delete this file if you're not using it