diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 17e509b..1733fa1 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -28,13 +28,13 @@ dependencies {
 // Apply a specific Java toolchain to ease working on different environments.
 java {
     toolchain {
-        languageVersion.set(JavaLanguageVersion.of(21))
+        languageVersion.set(JavaLanguageVersion.of(17))
     }
 }
 
 application {
     // Define the main class for the application.
-    mainClass.set("xl.App")
+    mainClass.set("gui.XL")
 }
 
 tasks.named<Test>("test") {