Add theme selection for code editor (#7375)

Change the theme selection of the code editor

Before
- was showing the window theme selector

After
- is showing the code editor theme selector


<img width="327" height="262" alt="image"
src="https://github.com/user-attachments/assets/50776218-26cc-4f11-9b91-6f902c022394"
/>


* [x] I have followed the instructions in the PR template

---------

Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui_extras/src/syntax_highlighting.rs

@@ -333,9 +333,19 @@ impl CodeTheme {
         }
     }
 
+    pub fn is_dark(&self) -> bool {
+        self.dark_mode
+    }
+
     /// Show UI for changing the color theme.
     pub fn ui(&mut self, ui: &mut egui::Ui) {
-        egui::widgets::global_theme_preference_buttons(ui);
+        ui.horizontal(|ui| {
+            ui.selectable_value(&mut self.dark_mode, true, "🌙 Dark theme")
+                .on_hover_text("Use the dark mode theme");
+
+            ui.selectable_value(&mut self.dark_mode, false, "☀ Light theme")
+                .on_hover_text("Use the light mode theme");
+        });
 
         for theme in SyntectTheme::all() {
             if theme.is_dark() == self.dark_mode {