gui: Add Dark Mode support with toggle switch

- Added dark.qss stylesheet for dark theme
- Implemented toggleTheme() slot in PalladiumGUI
- Added 'Dark Mode' checkbox to Settings menu
- Theme preference is saved in QSettings (darkModeEnabled)
- Updated palladium.qrc to include style resources

src/qt/palladium.qrc

@@ -83,4 +83,8 @@
         <file alias="spinner-034">res/movies/spinner-034.png</file>
         <file alias="spinner-035">res/movies/spinner-035.png</file>
     </qresource>
+
+    <qresource prefix="/">
+        <file>res/styles/dark.qss</file>
+    </qresource>
 </RCC>

src/qt/palladiumgui.cpp

@@ -61,6 +61,8 @@
 #include <QVBoxLayout>
 #include <QWindow>
 
+#include <QFile>
+#include <QTextStream>
 
 const std::string PalladiumGUI::DEFAULT_UIPLATFORM =
 #if defined(Q_OS_MAC)
@@ -79,7 +81,25 @@ PalladiumGUI::PalladiumGUI(interfaces::Node& node, const PlatformStyle *_platfor
     platformStyle(_platformStyle),
     m_network_style(networkStyle)
 {
+
+// --- DARK MODE AUTO-LOAD ---
     QSettings settings;
+    bool isDark = settings.value("darkModeEnabled", false).toBool();
+    if (isDark) {
+        // Stylesheet laden
+        QFile f(":/res/styles/dark.qss");
+        if (f.open(QFile::ReadOnly | QFile::Text)) {
+            QTextStream ts(&f);
+            qApp->setStyleSheet(ts.readAll());
+            f.close();
+        }
+        // Wichtig: Den Haken im Menü setzen!
+        if(themeAction) {
+             themeAction->setChecked(true);
+        }
+    }
+
+    //QSettings settings;
     if (!restoreGeometry(settings.value("MainWindowGeometry").toByteArray())) {
         // Restore failed (perhaps missing setting), center the window
         move(QGuiApplication::primaryScreen()->availableGeometry().center() - frameGeometry().center());
@@ -414,6 +434,10 @@ void PalladiumGUI::createActions()
 
     connect(new QShortcut(QKeySequence(Qt::CTRL + Qt::SHIFT + Qt::Key_C), this), &QShortcut::activated, this, &PalladiumGUI::showDebugWindowActivateConsole);
     connect(new QShortcut(QKeySequence(Qt::CTRL + Qt::SHIFT + Qt::Key_D), this), &QShortcut::activated, this, &PalladiumGUI::showDebugWindow);
+
+    themeAction = new QAction(tr("&Dark Mode"), this);
+    themeAction->setCheckable(true);
+    connect(themeAction, SIGNAL(triggered()), this, SLOT(toggleTheme()));
 }
 
 void PalladiumGUI::createMenuBar()
@@ -506,6 +530,8 @@ void PalladiumGUI::createMenuBar()
     help->addSeparator();
     help->addAction(aboutAction);
     help->addAction(aboutQtAction);
+
+    settings->addAction(themeAction);
 }
 
 void PalladiumGUI::createToolBars()
@@ -1463,3 +1489,23 @@ void UnitDisplayStatusBarControl::onMenuSelection(QAction* action)
         optionsModel->setDisplayUnit(action->data());
     }
 }
+void PalladiumGUI::toggleTheme()
+{
+    QSettings settings;
+    if (themeAction->isChecked()) {
+        // 1. Dark Mode laden
+        QFile f(":/res/styles/dark.qss");
+        if (f.open(QFile::ReadOnly | QFile::Text)) {
+            QTextStream ts(&f);
+            qApp->setStyleSheet(ts.readAll());
+            f.close();
+        }
+        // 2. Speichern, dass er an ist
+        settings.setValue("darkModeEnabled", true);
+    } else {
+        // 1. Standard Theme (Weiß)
+        qApp->setStyleSheet("");
+        // 2. Speichern, dass er aus ist
+        settings.setValue("darkModeEnabled", false);
+    }
+}

src/qt/palladiumgui.h

@@ -153,7 +153,7 @@ private:
     QAction* m_close_wallet_action{nullptr};
     QAction* m_wallet_selector_label_action = nullptr;
     QAction* m_wallet_selector_action = nullptr;
-
+    QAction *themeAction;
     QLabel *m_wallet_selector_label = nullptr;
     QComboBox* m_wallet_selector = nullptr;
 
@@ -308,6 +308,8 @@ public Q_SLOTS:
     void setTrayIconVisible(bool);
 
     void showModalOverlay();
+
+    void toggleTheme();
 };
 
 class UnitDisplayStatusBarControl : public QLabel

src/qt/res/styles/dark.qss

@@ -0,0 +1,146 @@
+/* =======================================================
+   PALLADIUM CORE DARK THEME (dark.qss)
+   ======================================================= */
+
+/* --- GRUNDLAGEN --- */
+QWidget {
+    background-color: #2D2D2D;
+    color: #E0E0E0;
+    selection-background-color: #007BFF;
+    selection-color: #FFFFFF;
+    outline: none;
+}
+
+/* --- MENÜLEISTE (Oben: File, Settings...) --- */
+QMenuBar {
+    background-color: #2D2D2D;
+    color: #E0E0E0;
+    border-bottom: 1px solid #3A3A3A;
+}
+
+QMenuBar::item {
+    background-color: transparent;
+    padding: 6px 10px;
+}
+
+QMenuBar::item:selected {
+    background-color: #3A3A3A;
+}
+
+QMenu {
+    background-color: #2D2D2D;
+    border: 1px solid #555;
+}
+
+QMenu::item {
+    padding: 5px 20px;
+}
+
+QMenu::item:selected {
+    background-color: #007BFF;
+    color: white;
+}
+
+/* --- TOOLBAR (Die Icons oben) --- */
+/* Wir machen sie etwas heller, damit schwarze Icons sichtbar bleiben */
+QToolBar {
+    background-color: #3D3D3D; 
+    border-bottom: 1px solid #3A3A3A;
+    padding: 2px;
+    spacing: 5px;
+}
+
+QToolButton {
+    background-color: transparent;
+    border: 1px solid transparent;
+    border-radius: 4px;
+    padding: 4px;
+    color: #E0E0E0;
+}
+
+QToolButton:hover {
+    background-color: #4D4D4D;
+    border: 1px solid #555;
+}
+
+QToolButton:checked {
+    background-color: #007BFF;
+    color: white;
+}
+
+/* --- TABS (Overview, Send, Receive) --- */
+QTabWidget::pane {
+    border: 1px solid #3A3A3A;
+}
+
+QTabBar::tab {
+    background: #1E1E1E;
+    color: #AAAAAA;
+    padding: 8px 20px;
+    border: 1px solid #3A3A3A;
+    border-bottom: none;
+    border-top-left-radius: 4px;
+    border-top-right-radius: 4px;
+    margin-right: 2px;
+}
+
+QTabBar::tab:selected {
+    background: #2D2D2D; /* Gleiche Farbe wie Hintergrund */
+    color: #FFFFFF;
+    border-bottom: 1px solid #2D2D2D; /* "Verbindet" den Tab mit dem Inhalt */
+    font-weight: bold;
+}
+
+/* --- EINGABEFELDER --- */
+QLineEdit, QTextEdit, QPlainTextEdit, QSpinBox, QDoubleSpinBox {
+    background-color: #1E1E1E;
+    color: #FFFFFF;
+    border: 1px solid #3A3A3A;
+    border-radius: 3px;
+    padding: 4px;
+}
+
+QLineEdit:focus {
+    border: 1px solid #007BFF;
+}
+
+/* --- LISTEN & TABELLEN (Transaktionen) --- */
+QTableView, QListView, QTreeWidget {
+    background-color: #1E1E1E;
+    alternate-background-color: #252525;
+    color: #E0E0E0;
+    gridline-color: #333;
+    border: 1px solid #3A3A3A;
+}
+
+QHeaderView::section {
+    background-color: #333;
+    color: #E0E0E0;
+    padding: 4px;
+    border: 1px solid #444;
+}
+
+/* --- BUTTONS --- */
+QPushButton {
+    background-color: #444;
+    border: 1px solid #555;
+    border-radius: 4px;
+    padding: 5px 15px;
+    color: white;
+}
+
+QPushButton:hover {
+    background-color: #555;
+}
+
+QPushButton:pressed {
+    background-color: #007BFF;
+    border-color: #007BFF;
+}
+
+/* --- STATUSBAR (Unten) --- */
+QStatusBar {
+    background-color: #2D2D2D;
+    color: #888;
+    border-top: 1px solid #3A3A3A;
+}