diff --git a/src/core/Config.cpp b/src/core/Config.cpp
index 41395214d..5965367b1 100644
--- a/src/core/Config.cpp
+++ b/src/core/Config.cpp
@@ -41,7 +41,7 @@ static const QMap<QString, QString> deprecationMap = {
     {QStringLiteral("security/IconDownloadFallbackToGoogle"), QStringLiteral("security/IconDownloadFallback")},
 };
 
-Config* Config::m_instance(nullptr);
+QPointer<Config> Config::m_instance(nullptr);
 
 QVariant Config::get(const QString& key)
 {
@@ -246,13 +246,17 @@ Config* Config::instance()
 
 void Config::createConfigFromFile(const QString& file)
 {
-    Q_ASSERT(!m_instance);
+    if (m_instance) {
+        delete m_instance;
+    }
     m_instance = new Config(file, qApp);
 }
 
 void Config::createTempFileInstance()
 {
-    Q_ASSERT(!m_instance);
+    if (m_instance) {
+        delete m_instance;
+    }
     auto* tmpFile = new QTemporaryFile();
     bool openResult = tmpFile->open();
     Q_ASSERT(openResult);
diff --git a/src/core/Config.h b/src/core/Config.h
index d65b3256b..ef6dd6af1 100644
--- a/src/core/Config.h
+++ b/src/core/Config.h
@@ -19,6 +19,7 @@
 #ifndef KEEPASSX_CONFIG_H
 #define KEEPASSX_CONFIG_H
 
+#include <QPointer>
 #include <QScopedPointer>
 #include <QVariant>
 
@@ -53,7 +54,7 @@ private:
     void init(const QString& fileName);
     void upgrade();
 
-    static Config* m_instance;
+    static QPointer<Config> m_instance;
 
     QScopedPointer<QSettings> m_settings;
     QHash<QString, QVariant> m_defaults;
diff --git a/src/gui/Application.cpp b/src/gui/Application.cpp
index b79f2c30a..7a2e956fc 100644
--- a/src/gui/Application.cpp
+++ b/src/gui/Application.cpp
@@ -18,8 +18,14 @@
  */
 
 #include "Application.h"
-#include "MainWindow.h"
+
+#include "autotype/AutoType.h"
 #include "core/Config.h"
+#include "core/Global.h"
+#include "gui/MainWindow.h"
+#include "gui/osutils/OSUtils.h"
+#include "gui/styles/dark/DarkStyle.h"
+#include "gui/styles/light/LightStyle.h"
 
 #include <QFileInfo>
 #include <QFileOpenEvent>
@@ -28,9 +34,6 @@
 #include <QStandardPaths>
 #include <QtNetwork/QLocalSocket>
 
-#include "autotype/AutoType.h"
-#include "core/Global.h"
-
 #if defined(Q_OS_WIN) || (defined(Q_OS_UNIX) && !defined(Q_OS_MACOS))
 #include "core/OSEventFilter.h"
 #endif
@@ -65,6 +68,26 @@ Application::Application(int& argc, char** argv)
     registerUnixSignals();
 #endif
 
+    QString appTheme = config()->get("GUI/ApplicationTheme").toString();
+    if (appTheme == "auto") {
+        if (osUtils->isDarkMode()) {
+            setStyle(new DarkStyle);
+            m_darkTheme = true;
+        } else {
+            setStyle(new LightStyle);
+        }
+    } else if (appTheme == "light") {
+        setStyle(new LightStyle);
+    } else if (appTheme == "dark") {
+        setStyle(new DarkStyle);
+        m_darkTheme = true;
+    } else {
+        // Classic mode, only check for dark theme when not on Windows
+#ifndef Q_OS_WIN
+        m_darkTheme = osUtils->isDarkMode();
+#endif
+    }
+
     QString userName = qgetenv("USER");
     if (userName.isEmpty()) {
         userName = qgetenv("USERNAME");
@@ -281,3 +304,8 @@ bool Application::sendFileNamesToRunningInstance(const QStringList& fileNames)
     const bool disconnected = client.waitForDisconnected(WaitTimeoutMSec);
     return writeOk && disconnected;
 }
+
+bool Application::isDarkTheme() const
+{
+    return m_darkTheme;
+}
diff --git a/src/gui/Application.h b/src/gui/Application.h
index 9a3ef756b..b39fbe0e9 100644
--- a/src/gui/Application.h
+++ b/src/gui/Application.h
@@ -41,6 +41,7 @@ public:
 
     bool event(QEvent* event) override;
     bool isAlreadyRunning() const;
+    bool isDarkTheme() const;
 
     bool sendFileNamesToRunningInstance(const QStringList& fileNames);
 
@@ -68,6 +69,7 @@ private:
     static int unixSignalSocket[2];
 #endif
     bool m_alreadyRunning;
+    bool m_darkTheme = false;
     QLockFile* m_lockFile;
     QLocalServer m_lockServer;
     QString m_socketName;
@@ -76,4 +78,6 @@ private:
 #endif
 };
 
+#define kpxcApp qobject_cast<Application*>(Application::instance())
+
 #endif // KEEPASSX_APPLICATION_H
diff --git a/src/main.cpp b/src/main.cpp
index 524f112b3..c3494f02f 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -29,9 +29,6 @@
 #include "gui/Application.h"
 #include "gui/MainWindow.h"
 #include "gui/MessageBox.h"
-#include "gui/osutils/OSUtils.h"
-#include "gui/styles/dark/DarkStyle.h"
-#include "gui/styles/light/LightStyle.h"
 
 #if defined(WITH_ASAN) && defined(WITH_LSAN)
 #include <sanitizer/lsan_interface.h>
@@ -64,19 +61,6 @@ int main(int argc, char** argv)
     Application::setApplicationName("KeePassXC");
     Application::setApplicationVersion(KEEPASSXC_VERSION);
 
-    QString appTheme = config()->get("GUI/ApplicationTheme").toString();
-    if (appTheme == "auto") {
-        if (osUtils->isDarkMode()) {
-            QApplication::setStyle(new DarkStyle);
-        } else {
-            QApplication::setStyle(new LightStyle);
-        }
-    } else if (appTheme == "light") {
-        QApplication::setStyle(new LightStyle);
-    } else if (appTheme == "dark") {
-        QApplication::setStyle(new DarkStyle);
-    }
-
     // don't set organizationName as that changes the return value of
     // QStandardPaths::writableLocation(QDesktopServices::DataLocation)
     Bootstrap::bootstrapApplication();
diff --git a/tests/gui/TestGui.cpp b/tests/gui/TestGui.cpp
index 8ce9b0587..76766c8dc 100644
--- a/tests/gui/TestGui.cpp
+++ b/tests/gui/TestGui.cpp
@@ -74,16 +74,27 @@
 #include "keys/FileKey.h"
 #include "keys/PasswordKey.h"
 
-QTEST_MAIN(TestGui)
+int main(int argc, char* argv[])
+{
+#if QT_VERSION >= QT_VERSION_CHECK(5, 6, 0)
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
+    Application app(argc, argv);
+    app.setApplicationName("KeePassXC");
+    app.setApplicationVersion(KEEPASSXC_VERSION);
+    app.setQuitOnLastWindowClosed(false);
+    app.setAttribute(Qt::AA_Use96Dpi, true);
+    QTEST_DISABLE_KEYPAD_NAVIGATION
+    TestGui tc;
+    QTEST_SET_MAIN_SOURCE_PATH
+    return QTest::qExec(&tc, argc, argv);
+}
 
 static QString dbFileName = QStringLiteral(KEEPASSX_TEST_DATA_DIR).append("/NewDatabase.kdbx");
 
 void TestGui::initTestCase()
 {
-    Application::setApplicationName("KeePassXC");
-    Application::setApplicationVersion(KEEPASSXC_VERSION);
-    QApplication::setQuitOnLastWindowClosed(false);
-
     QVERIFY(Crypto::init());
     Config::createTempFileInstance();
     // Disable autosave so we can test the modified file indicator
diff --git a/tests/gui/TestGuiBrowser.cpp b/tests/gui/TestGuiBrowser.cpp
index 834aea581..1750caa80 100644
--- a/tests/gui/TestGuiBrowser.cpp
+++ b/tests/gui/TestGuiBrowser.cpp
@@ -47,7 +47,22 @@
 #include "gui/entry/EditEntryWidget.h"
 #include "gui/entry/EntryView.h"
 
-QTEST_MAIN(TestGuiBrowser)
+int main(int argc, char* argv[])
+{
+#if QT_VERSION >= QT_VERSION_CHECK(5, 6, 0)
+    QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+    QGuiApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
+#endif
+    Application app(argc, argv);
+    app.setApplicationName("KeePassXC");
+    app.setApplicationVersion(KEEPASSXC_VERSION);
+    app.setQuitOnLastWindowClosed(false);
+    app.setAttribute(Qt::AA_Use96Dpi, true);
+    QTEST_DISABLE_KEYPAD_NAVIGATION
+    TestGuiBrowser tc;
+    QTEST_SET_MAIN_SOURCE_PATH
+    return QTest::qExec(&tc, argc, argv);
+}
 
 void TestGuiBrowser::initTestCase()
 {