General source code refactoring

src/content/theme.js

@@ -0,0 +1,32 @@
+function createContentTheme({
+  THEME_STORAGE_KEY,
+  createThemeIcon,
+  environment
+}) {
+  const getLocalStorage = () => environment.localStorage;
+  function getSavedTheme() {
+    try {
+      return getLocalStorage().getItem(THEME_STORAGE_KEY) === "dark" ? "dark" : "light";
+    } catch (error) {
+      return "light";
+    }
+  }
+
+  function applyTheme(modal, button, theme) {
+    const isDarkTheme = theme === "dark";
+
+    modal.setAttribute("data-theme", isDarkTheme ? "dark" : "light");
+    button.textContent = "";
+    button.setAttribute("aria-label", isDarkTheme ? "Ativar modo claro" : "Ativar modo escuro");
+    button.title = isDarkTheme ? "Light mode" : "Dark mode";
+    button.append(createThemeIcon(isDarkTheme ? "sun" : "moon"));
+
+    try {
+      getLocalStorage().setItem(THEME_STORAGE_KEY, isDarkTheme ? "dark" : "light");
+    } catch (error) {
+      // Continue with the selected theme when browser storage is unavailable.
+    }
+  }
+
+  return { getSavedTheme, applyTheme };
+}