All TODOS done

src/main/java/app/Main.java

@@ -4,6 +4,7 @@ import java.io.IOException;
 import java.util.Optional;
 
 import javafx.application.Application;
+import javafx.application.Platform;
 import javafx.fxml.FXMLLoader;
 import javafx.scene.Parent;
 import javafx.scene.Scene;
@@ -11,6 +12,7 @@ import javafx.scene.image.Image;
 import javafx.stage.Stage;
 import app.events.FileSaveStateChangedEvent;
 import app.model.Model;
+import app.service.DialogBoxes;
 import app.settings.SettingsProvider;
 
 public class Main extends Application {
@@ -46,10 +48,15 @@ public class Main extends Application {
    * 
    * @throws IOException
    */
-  private void loadFXML() throws IOException {
-    // TODO: Error handle this function.
-    this.fxmlLoader = new FXMLLoader(getClass().getResource("/fxml/Main.fxml"));
-    this.fxmlRoot = fxmlLoader.load();
+  private void loadFXML() {
+    try {
+      this.fxmlLoader = new FXMLLoader(getClass().getResource("/fxml/Main.fxml"));
+      this.fxmlRoot = fxmlLoader.load();
+    } catch (Exception e) {
+      DialogBoxes.showErrorMessage("There is an error within the program. Please try to reinstall.");
+      System.exit(1);
+    }
+
   }
 
   /**

src/main/java/app/MainController.java

@@ -93,7 +93,9 @@ public class MainController implements Initializable {
    * @param cssPath  The path in resources to the new CSS file
    */
   private void setCSSAt(int position, String cssPath) {
-    // TODO: Error check that position in range 0 to 1
+    if ((position != 0) && (position != 1)) {
+      throw new IllegalArgumentException("Range of position must be either 0 or 1");
+    } 
     String nextStyleSheet = getClass().getResource(cssPath).toExternalForm();
 
     Model.getScene().getStylesheets().set(position, nextStyleSheet);