diff --git a/CMakeLists.txt b/CMakeLists.txt
index 5d63dc0..72319ce 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -4,30 +4,30 @@ project(project-kyoku LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 14)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -g")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -Wextra -Wpedantic -g")
 set(CMAKE_THREAD_LIBS_INIT "-lpthread")
       SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
       set(CMAKE_HAVE_THREADS_LIBRARY 1)
       set(CMAKE_USE_WIN32_THREADS_INIT 0)
       set(CMAKE_USE_PTHREADS_INIT 1)
       set(THREADS_PREFER_PTHREAD_FLAG ON)
-file(GLOB SOURCES "src/*.cpp" "src/classicgame/*.*" "src/classicgame/classicnotestate/*")
+file(GLOB_RECURSE SOURCES "src/*.cpp" "src/*.h")
 
 # STATIC #
 # You need to build SFML from sources with cmake
-#set(SFML_LIB_DIR
-#    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-graphics.so.2.5
-#    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-system.so.2.5
-#    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-window.so.2.5
-#    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-audio.so.2.5)
-#set(SFML_INCL_DIR ${CMAKE_SOURCE_DIR}/SFML-2.5.1/include)
-#include_directories(${SFML_INCL_DIR} ${CMAKE_SOURCE_DIR}/include)
-#add_executable(project-kyoku ${SOURCES})
-#target_link_libraries(project-kyoku ${SFML_LIB_DIR})
+set(SFML_LIB_DIR
+    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-graphics.so.2.5
+    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-system.so.2.5
+    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-window.so.2.5
+    ${CMAKE_SOURCE_DIR}/SFML-2.5.1/lib/libsfml-audio.so.2.5)
+set(SFML_INCL_DIR ${CMAKE_SOURCE_DIR}/SFML-2.5.1/include)
+include_directories(${SFML_INCL_DIR} ${CMAKE_SOURCE_DIR}/include)
+add_executable(project-kyoku ${SOURCES})
+target_link_libraries(project-kyoku ${SFML_LIB_DIR})
 
 # DYNAMIC #
 # You only need to install SFML from your package manager
-find_package(SFML REQUIRED graphics window system)
-add_executable(project-kyoku ${SOURCES})
-include_directories(${SFML_INCL_DIR} ${CMAKE_SOURCE_DIR}/include)
-target_link_libraries(project-kyoku sfml-system sfml-audio sfml-graphics sfml-network)
+#find_package(SFML REQUIRED graphics window system)
+#add_executable(project-kyoku ${SOURCES})
+#include_directories(${SFML_INCL_DIR} ${CMAKE_SOURCE_DIR}/include)
+#target_link_libraries(project-kyoku sfml-system sfml-audio sfml-graphics sfml-network)
diff --git a/include/gui/state.h b/include/gui/state.h
index f0f3610..398be7e 100644
--- a/include/gui/state.h
+++ b/include/gui/state.h
@@ -7,9 +7,10 @@
 
 class GUIState : public sf::Drawable
 {
+public:
     virtual ~GUIState() = default;
 
-    virtual void input(const sf::Event& event, std::stack<std::shared_ptr<GUIState>>& states) = 0;
+    virtual void input(const sf::Event& event) = 0;
     virtual void update() = 0;
     virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const = 0;
 };
diff --git a/src/application.cpp b/src/application.cpp
index 4a426d5..c5f59a9 100644
--- a/src/application.cpp
+++ b/src/application.cpp
@@ -4,6 +4,8 @@
 #include "classicgame/classicgame.h"
 #include "classicgame/classicgraphicsmanager.h"
 
+#include "gui/mainmenu.h"
+
 #include <iostream>
 
 const sf::Time TIME_PER_FRAME = sf::seconds(1.f / 90.f);
@@ -16,12 +18,13 @@ Application::Application() :
     _game_window.setKeyRepeatEnabled(false);
     _game_window.setMouseCursorGrabbed(false);
     _game_window.setVerticalSyncEnabled(true);
+
+    _states.push(std::make_shared<MainMenu>(_game_window));
 }
 
 void Application::run()
 {
     _game_window.display();
-    _game->run();
 
     exec();
 }
@@ -60,9 +63,11 @@ void Application::input()
 
         case sf::Event::KeyPressed:
         case sf::Event::KeyReleased:
+        case sf::Event::MouseButtonReleased:
+        case sf::Event::MouseButtonPressed:
             if (event.key.code == sf::Keyboard::Escape)
                 _game_window.close();
-            _game->input(PlayerInput{0, event});
+            _states.top()->input(event);
             break;
 
         default:
@@ -73,12 +78,12 @@ void Application::input()
 
 void Application::update()
 {
-    _game->update();
+    _states.top()->update();
 }
 
 void Application::draw()
 {
     _game_window.clear();
-    _game->draw();
+    _game_window.draw(*_states.top());
     _game_window.display();
 }
diff --git a/src/classicgame/classicdyinganimationscenario.cpp b/src/classicgame/classicdyinganimationscenario.cpp
index cae1aee..926611c 100644
--- a/src/classicgame/classicdyinganimationscenario.cpp
+++ b/src/classicgame/classicdyinganimationscenario.cpp
@@ -12,6 +12,7 @@ void ClassicDyingAnimationScenario::launch(const std::shared_ptr<ClassicSprite>
 
 void ClassicDyingAnimationScenario::update(const microsec& music_offset)
 {
+    (void) music_offset;
     _sprite->update();
 }
 
diff --git a/src/gui/button.cpp b/src/gui/button.cpp
deleted file mode 100644
index 49cc11c..0000000
--- a/src/gui/button.cpp
+++ /dev/null
@@ -1,48 +0,0 @@
-#include "button.h"
-
-Button::Button(const std::string &text)
-{
-    _button_text.setString(text);
-    _button_text.setFillColor(sf::Color::Black);
-    _button_content.setFillColor(sf::Color::White);
-}
-
-void Button::input(const sf::Event& event)
-{
-    switch (event.type)
-    {
-    case sf::Event::MouseButtonPressed:
-        break;
-    }
-}
-
-void Button::update()
-{
-
-}
-
-void Button::draw(sf::RenderTarget& target, sf::RenderStates states) const
-{
-
-}
-
-void Button::setRect(const sf::IntRect& rect)
-{
-
-}
-
-void Button::setPosition(const sf::Vector2f& position)
-{
-
-}
-
-void Button::setText(const std::string& text)
-{
-
-}
-
-void Button::setCallback(std::function<void(void)> callback)
-{
-
-}
-
diff --git a/src/gui/mainmenu.cpp b/src/gui/mainmenu.cpp
new file mode 100644
index 0000000..818b217
--- /dev/null
+++ b/src/gui/mainmenu.cpp
@@ -0,0 +1,41 @@
+#include "mainmenu.h"
+#include "widgets/button.h"
+#include "widgets/group.h"
+
+MainMenu::MainMenu(sf::RenderWindow& game_window) :
+    _buttons(std::make_shared<Group>()),
+    _game_window(game_window)
+{
+    std::shared_ptr<Button> button_start = std::make_shared<Button>("Start");
+    button_start->setRect(sf::FloatRect(140, 140, 500, 100));
+    button_start->setCallback([&]()
+    {
+        _game_window.close();
+    });
+
+    std::shared_ptr<Button> button_exit = std::make_shared<Button>("Exit");
+    button_exit->setRect(sf::FloatRect(140, 140, 400, 100));
+    button_exit->setPosition({240, 340});
+    button_exit->setCallback([&]()
+    {
+        _game_window.close();
+    });
+
+    _buttons->addChild(button_start);
+    _buttons->addChild(button_exit);
+}
+
+void MainMenu::input(const sf::Event& event)
+{
+    _buttons->input(event);
+}
+
+void MainMenu::update()
+{
+    _buttons->update();
+}
+
+void MainMenu::draw(sf::RenderTarget& target, sf::RenderStates states) const
+{
+    target.draw(*_buttons, states);
+}
diff --git a/src/gui/mainmenu.h b/src/gui/mainmenu.h
new file mode 100644
index 0000000..b75bea5
--- /dev/null
+++ b/src/gui/mainmenu.h
@@ -0,0 +1,20 @@
+#pragma once
+
+#include "gui/state.h"
+#include <SFML/Graphics/RenderWindow.hpp>
+
+class Group;
+
+class MainMenu : public GUIState
+{
+public:
+    MainMenu(sf::RenderWindow& game_window);
+    virtual void input(const sf::Event& event) override;
+    virtual void update() override;
+    virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const override;
+
+private:
+    std::shared_ptr<Group> _buttons;
+    sf::RenderWindow& _game_window;
+};
+
diff --git a/src/gui/widget.cpp b/src/gui/widget.cpp
deleted file mode 100644
index 1de6e3c..0000000
--- a/src/gui/widget.cpp
+++ /dev/null
@@ -1,13 +0,0 @@
-#include "widget.h"
-
-Widget::Widget(const std::shared_ptr<Widget>& parent) :
-    _parent(parent)
-{
-    if (_parent)
-        _parent->addChild(shared_from_this());
-}
-
-void Widget::addChild(const std::shared_ptr<Widget> &child)
-{
-    _children.emplace_back(child);
-}
diff --git a/src/gui/widgets/button.cpp b/src/gui/widgets/button.cpp
new file mode 100644
index 0000000..d559d7c
--- /dev/null
+++ b/src/gui/widgets/button.cpp
@@ -0,0 +1,78 @@
+#include "button.h"
+
+Button::Button(const std::string &text) :
+    _pressed(false)
+{
+    setText(text);
+    _button_text.setFillColor(sf::Color::Black);
+    _button_content.setFillColor(sf::Color::White);
+}
+
+void Button::input(const sf::Event& event)
+{
+    switch (event.type)
+    {
+    default:
+        break;
+
+    case sf::Event::MouseButtonPressed:
+        if (isUnderMouse(event.mouseButton.x, event.mouseButton.y))
+        {
+            _pressed = true;
+            _button_content.setFillColor(sf::Color(155, 155, 155));
+        }
+        break;
+
+    case sf::Event::MouseButtonReleased:
+        if (_pressed)
+        {
+            _button_content.setFillColor(sf::Color::White);
+            _pressed = false;
+            if (isUnderMouse(event.mouseButton.x, event.mouseButton.y))
+                _on_click_callback();
+        }
+        break;
+    }
+
+    Widget::input(event);
+}
+
+void Button::update()
+{
+    Widget::update();
+}
+
+void Button::draw(sf::RenderTarget& target, sf::RenderStates states) const
+{
+    target.draw(_button_content, states);
+    target.draw(_button_text, states);
+
+    Widget::draw(target, states);
+}
+
+void Button::setRect(const sf::FloatRect& rect)
+{
+    _button_content.setPosition(rect.left, rect.top);
+    _button_content.setSize({rect.width - rect.left, rect.height - rect.top});
+}
+
+void Button::setPosition(const sf::Vector2f &position)
+{
+    _button_content.setPosition(position);
+}
+
+bool Button::isUnderMouse(int mouse_x, int mouse_y) const
+{
+    return _button_content.getGlobalBounds().contains(mouse_x, mouse_y);
+}
+
+void Button::setText(const std::string& text)
+{
+    _button_text.setString(text);
+}
+
+void Button::setCallback(std::function<void(void)> callback)
+{
+    _on_click_callback = callback;
+}
+
diff --git a/src/gui/button.h b/src/gui/widgets/button.h
similarity index 76%
rename from src/gui/button.h
rename to src/gui/widgets/button.h
index e85e8e3..44236c2 100644
--- a/src/gui/button.h
+++ b/src/gui/widgets/button.h
@@ -13,8 +13,9 @@ public:
     virtual void input(const sf::Event& event) override;
     virtual void update() override;
     virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const override;
-    virtual void setRect(const sf::IntRect& rect) override;
+    virtual void setRect(const sf::FloatRect& rect) override;
     virtual void setPosition(const sf::Vector2f& position) override;
+    virtual bool isUnderMouse(int mouse_x, int mouse_y) const override;
 
     void setText(const std::string& text);
     void setCallback(std::function<void(void)> callback);
@@ -22,5 +23,8 @@ public:
 private:
     sf::RectangleShape _button_content;
     sf::Text _button_text;
+    bool _pressed;
+
+    std::function<void(void)> _on_click_callback;
 };
 
diff --git a/src/gui/widgets/group.cpp b/src/gui/widgets/group.cpp
new file mode 100644
index 0000000..645a2e8
--- /dev/null
+++ b/src/gui/widgets/group.cpp
@@ -0,0 +1,32 @@
+#include "group.h"
+
+void Group::input(const sf::Event& event)
+{
+    Widget::input(event);
+}
+
+void Group::update()
+{
+    Widget::update();
+}
+
+void Group::draw(sf::RenderTarget& target, sf::RenderStates states) const
+{
+    Widget::draw(target, states);
+}
+
+void Group::setRect(const sf::FloatRect& rect)
+{
+    _rect = rect;
+}
+
+void Group::setPosition(const sf::Vector2f& position)
+{
+    _rect.top = position.y;
+    _rect.left = position.x;
+}
+
+bool Group::isUnderMouse(int mouse_x, int mouse_y) const
+{
+   return _rect.contains(mouse_x, mouse_y);
+}
diff --git a/src/gui/widgets/group.h b/src/gui/widgets/group.h
new file mode 100644
index 0000000..8ebe145
--- /dev/null
+++ b/src/gui/widgets/group.h
@@ -0,0 +1,18 @@
+#pragma once
+
+#include "widget.h"
+
+class Group : public Widget
+{
+public:
+    virtual void input(const sf::Event& event) override;
+    virtual void update() override;
+    virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const override;
+    virtual void setRect(const sf::FloatRect& rect) override;
+    virtual void setPosition(const sf::Vector2f& position) override;
+    virtual bool isUnderMouse(int mouse_x, int mouse_y) const override;
+
+private:
+    sf::FloatRect _rect;
+};
+
diff --git a/src/gui/widgets/widget.cpp b/src/gui/widgets/widget.cpp
new file mode 100644
index 0000000..12c5727
--- /dev/null
+++ b/src/gui/widgets/widget.cpp
@@ -0,0 +1,25 @@
+#include "widget.h"
+
+void Widget::input(const sf::Event &event)
+{
+    for (auto& child : _children)
+        child->input(event);
+}
+
+void Widget::update()
+{
+    for (auto& child : _children)
+        child->update();
+}
+
+void Widget::draw(sf::RenderTarget& target, sf::RenderStates states) const
+{
+    for (auto& child : _children)
+        child->draw(target, states);
+}
+
+void Widget::addChild(const std::shared_ptr<Widget> &child)
+{
+    child->_parent = shared_from_this();
+    _children.emplace_back(child);
+}
diff --git a/src/gui/widget.h b/src/gui/widgets/widget.h
similarity index 71%
rename from src/gui/widget.h
rename to src/gui/widgets/widget.h
index 3c3c265..ef2cc8f 100644
--- a/src/gui/widget.h
+++ b/src/gui/widgets/widget.h
@@ -4,12 +4,11 @@
 #include <memory>
 #include <SFML/Window/Event.hpp>
 #include <SFML/Graphics/Drawable.hpp>
+#include <SFML/Graphics/RenderTarget.hpp>
 
-class Widget : public sf::Drawable, std::enable_shared_from_this<Widget>
+class Widget : public sf::Drawable, public std::enable_shared_from_this<Widget>
 {
 public:
-    Widget(const std::shared_ptr<Widget>& parent = nullptr);
-
     virtual ~Widget() = default;
 
     virtual void input(const sf::Event& event) = 0;
@@ -17,11 +16,12 @@ public:
     virtual void draw(sf::RenderTarget& target, sf::RenderStates states) const = 0;
     virtual void setRect(const sf::FloatRect& rect) = 0;
     virtual void setPosition(const sf::Vector2f& position) = 0;
+    virtual bool isUnderMouse(int mouse_x, int mouse_y) const = 0;
 
-protected:
     void addChild(const std::shared_ptr<Widget>& child);
 
+protected:
     std::vector<std::shared_ptr<Widget>> _children;
-    const std::shared_ptr<Widget> _parent;
+    std::shared_ptr<Widget> _parent;
 };