diff --git a/Makefile b/Makefile
index d08b524..d90ddf7 100644
--- a/Makefile
+++ b/Makefile
@@ -6,8 +6,8 @@ TARGET = matemateak
 CFLAGS = -std=c17 -Wall -Wextra -Wpedantic -Wconversion
 LFLAGS = -lm
 
-CFLAGS += $(shell pkg-config --cflags gtk+-2.0)
-LFLAGS += $(shell pkg-config --libs gtk+-2.0)
+CFLAGS += $(shell pkg-config --cflags gtk+-3.0)
+LFLAGS += $(shell pkg-config --libs gtk+-3.0)
 
 C_FILES = $(shell find src/ -name *.c)
 HEADER_FILES = $(shell find src/ -name *.h)
diff --git a/src/main.c b/src/main.c
index 2a55811..dd358d0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,75 +1,38 @@
-#include "lexer.h"
-#include "parser.h"
 #include <gtk/gtk.h>
 #include <stdio.h>
 #include <stdlib.h>
-#include <string.h>
 
-void test_lexer_parser(void)
+static void button_handler(GtkWidget* widget, gpointer user_data)
 {
-    char* text = "2 * (3 + 4)";
+    g_print("Button pressed!\n");
+}
 
-    Lexer lexer1;
-    lexer(&lexer1, text, strlen(text));
-    Token current_token = lexer_next(&lexer1);
-    printf("tokens = [\n");
-    while (current_token.type != TokenTypeEof) {
-        char* token_string = token_to_string(&current_token, text);
-        printf("    %s,\n", token_string);
-        free(token_string);
-        current_token = lexer_next(&lexer1);
-    }
-    printf("]\n");
+static void activate(GtkApplication* app, gpointer user_data)
+{
+    GtkWidget* window = gtk_application_window_new(app);
+    gtk_window_set_title(GTK_WINDOW(window), "MatemaTeak");
+    gtk_window_set_default_size(GTK_WINDOW(window), 1600, 900);
 
-    Lexer lexer2;
-    lexer(&lexer2, text, strlen(text));
-    Expr* ast = parse(&lexer2, text, strlen(text));
-    char* ast_string = expr_to_string(ast);
-    printf("ast = %s\n", ast_string);
-    free(ast_string);
-    free_expr(ast);
+    GtkWidget* button_box = gtk_button_box_new(GTK_ORIENTATION_HORIZONTAL);
+    gtk_container_add(GTK_CONTAINER(window), button_box);
+
+    GtkWidget* button = gtk_button_new_with_label("Do stuff");
+    g_signal_connect(button, "clicked", G_CALLBACK(button_handler), NULL);
+    g_signal_connect_swapped(
+        button, "clicked", G_CALLBACK(gtk_widget_destroy), window
+    );
+    gtk_container_add(GTK_CONTAINER(button_box), button);
+
+    gtk_widget_show_all(window);
 }
 
 int main(int argc, char** argv)
 {
-    GtkWidget* window;
-    GtkWidget* vbox;
-
-    GtkWidget* menubar;
-    GtkWidget* fileMenu;
-    GtkWidget* fileMi;
-    GtkWidget* quitMi;
-
-    gtk_init(&argc, &argv);
-
-    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
-    gtk_window_set_position(GTK_WINDOW(window), GTK_WIN_POS_CENTER);
-    gtk_window_set_default_size(GTK_WINDOW(window), 300, 200);
-    gtk_window_set_title(GTK_WINDOW(window), "Simple menu");
-
-    vbox = gtk_vbox_new(FALSE, 0);
-    gtk_container_add(GTK_CONTAINER(window), vbox);
-
-    menubar = gtk_menu_bar_new();
-    fileMenu = gtk_menu_new();
-
-    fileMi = gtk_menu_item_new_with_label("File");
-    quitMi = gtk_menu_item_new_with_label("Quit");
-
-    gtk_menu_item_set_submenu(GTK_MENU_ITEM(fileMi), fileMenu);
-    gtk_menu_shell_append(GTK_MENU_SHELL(fileMenu), quitMi);
-    gtk_menu_shell_append(GTK_MENU_SHELL(menubar), fileMi);
-    gtk_box_pack_start(GTK_BOX(vbox), menubar, FALSE, FALSE, 0);
-
-    g_signal_connect(
-        G_OBJECT(window), "destroy", G_CALLBACK(gtk_main_quit), NULL
+    GtkApplication* app = gtk_application_new(
+        "dk.simonfj20.matemateak", G_APPLICATION_DEFAULT_FLAGS
     );
-
-    g_signal_connect(
-        G_OBJECT(quitMi), "activate", G_CALLBACK(gtk_main_quit), NULL
-    );
-
-    gtk_widget_show_all(window);
-
-    gtk_main();
+    g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
+    int status = g_application_run(G_APPLICATION(app), argc, argv);
+    g_object_unref(app);
+    return status;
 }
diff --git a/src/parser_test.c b/src/parser_test.c
new file mode 100644
index 0000000..bcc8ce9
--- /dev/null
+++ b/src/parser_test.c
@@ -0,0 +1,30 @@
+#include "lexer.h"
+#include "parser.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void test_lexer_parser(void)
+{
+    char* text = "2 * (3 + 4)";
+
+    Lexer lexer1;
+    lexer(&lexer1, text, strlen(text));
+    Token current_token = lexer_next(&lexer1);
+    printf("tokens = [\n");
+    while (current_token.type != TokenTypeEof) {
+        char* token_string = token_to_string(&current_token, text);
+        printf("    %s,\n", token_string);
+        free(token_string);
+        current_token = lexer_next(&lexer1);
+    }
+    printf("]\n");
+
+    Lexer lexer2;
+    lexer(&lexer2, text, strlen(text));
+    Expr* ast = parse(&lexer2, text, strlen(text));
+    char* ast_string = expr_to_string(ast);
+    printf("ast = %s\n", ast_string);
+    free(ast_string);
+    free_expr(ast);
+}