Update reflectColorPreference to apply web awesome's wa-dark class

* Web Awesome provides its own `wa-dark` class to trigger dark mode,
	which we need `reflectColorPreference` to use
	* See: https://backers.webawesome.com/docs/themes/classic#dark-mode

Author: tcannonfodder

src/util/theme-preference.js

@@ -21,7 +21,16 @@ export function setColorPreference(value){
 }
 
 export function reflectColorPreference(){
-  document.firstElementChild.setAttribute(htmlDataAttributeName, getColorPreference())
+  const preference = getColorPreference()
+  const browserPrefersDark = window.matchMedia(`(prefers-color-scheme:dark)`).matches
+  const forcedDarkMode = preference == "dark"
+  const systemMatchMode = preference == "match-system" && browserPrefersDark
+
+  if(forcedDarkMode || systemMatchMode) {
+    document.firstElementChild.classList.add("wa-dark")
+  } else {
+    document.firstElementChild.classList.remove("wa-dark")
+  }
 }
 
 
@@ -30,4 +39,4 @@ export function setDefaultColorPreference(defaultValue){
   if(!localStorage){ return }
   if(localStorage.getItem(storageKey)){ return }
   setColorPreference(defaultValue)
-}
+}