Update color-modes.js (#38626)

* Update color-modes.js

Fix IF statement in the prefer-color-scheme change listener always evaluating to `true` and changing the theme to "dark" even when "light" is set as the preferred theme.

| `||` | `x !== "light"` | `x !== "dark"` | Result |
|--|:--:|:--:|:--:|
| `x = "light"` | ○ | ● | ● |
| `x = "dark"` | ● | ○ | ● |
| `x = "auto"` | ● | ● | ● |
| `x = "bogus"` | ● | ● | ● |
<hr>

| `&&` | `x !== "light"` | `x !== "dark"` | Result |
|--|:--:|:--:|:--:|
| `x = "light"` | ○ | ● | ○ |
| `x = "dark"` | ● | ○ | ○ |
| `x = "auto"` | ● | ● | ● |
| `x = "bogus"` | ● | ● | ● |

* Implement re-read of stored theme

site/static/docs/5.3/assets/js/color-modes.js

@@ -7,17 +7,19 @@
 (() => {
   'use strict'
 
-  const storedTheme = localStorage.getItem('theme')
+  const getStoredTheme = () => localStorage.getItem('theme')
+  const setStoredTheme = theme => localStorage.setItem('theme', theme)
 
   const getPreferredTheme = () => {
+    const storedTheme = getStoredTheme()
     if (storedTheme) {
       return storedTheme
     }
 
     return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light'
   }
 
-  const setTheme = function (theme) {
+  const setTheme = theme => {
     if (theme === 'auto' && window.matchMedia('(prefers-color-scheme: dark)').matches) {
       document.documentElement.setAttribute('data-bs-theme', 'dark')
     } else {
@@ -56,6 +58,7 @@
   }
 
   window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', () => {
+    const storedTheme = getStoredTheme()
     if (storedTheme !== 'light' || storedTheme !== 'dark') {
       setTheme(getPreferredTheme())
     }
@@ -68,7 +71,7 @@
       .forEach(toggle => {
         toggle.addEventListener('click', () => {
           const theme = toggle.getAttribute('data-bs-theme-value')
-          localStorage.setItem('theme', theme)
+          setStoredTheme(theme)
           setTheme(theme)
           showActiveTheme(theme, true)
         })