Minor theme fixes

* Support mouse hover color change for QPushButtons.
* Fix #5040 - don't enforce standard palette when in classic theme mode

src/gui/Application.cpp

@@ -144,18 +144,19 @@ Application::~Application()
 
 void Application::applyTheme()
 {
-    QString appTheme = config()->get(Config::GUI_ApplicationTheme).toString();
+    auto appTheme = config()->get(Config::GUI_ApplicationTheme).toString();
     if (appTheme == "auto") {
-        if (osUtils->isDarkMode()) {
-            setStyle(new DarkStyle);
-            m_darkTheme = true;
-        } else {
-            setStyle(new LightStyle);
-        }
-    } else if (appTheme == "light") {
+        appTheme = osUtils->isDarkMode() ? "dark" : "light";
+    }
+
+    if (appTheme == "light") {
         setStyle(new LightStyle);
+        // Workaround Qt 5.15+ bug
+        setPalette(style()->standardPalette());
     } else if (appTheme == "dark") {
         setStyle(new DarkStyle);
+        // Workaround Qt 5.15+ bug
+        setPalette(style()->standardPalette());
         m_darkTheme = true;
     } else {
         // Classic mode, don't check for dark theme on Windows
@@ -164,8 +165,6 @@ void Application::applyTheme()
         m_darkTheme = osUtils->isDarkMode();
 #endif
     }
-
-    setPalette(style()->standardPalette());
 }
 
 bool Application::event(QEvent* event)

src/gui/styles/base/basestyle.qss

@@ -3,6 +3,11 @@ QPushButton:default {
     color: palette(highlighted-text);
 }
 
+/* Note: default button hover is defined in the respective theme style */
+QPushButton:!default:hover {
+    background: palette(mid);
+}
+
 QSpinBox {
     min-width: 90px;
 }

src/gui/styles/dark/darkstyle.qss

@@ -8,6 +8,16 @@ EntryPreviewWidget QLineEdit:disabled, EntryPreviewWidget QTextEdit:disabled {
     background-color: #424242;
 }
 
+QPushButton:!default:hover {
+    /* Using slightly darker shade from palette(button) */
+    background: #252528;
+}
+
+QPushButton:default:hover {
+    /* Using slightly lighter shade from palette(highlight) */
+    background: #2E582E;
+}
+
 QToolTip {
     color: #BFBFBF;
     background-color: #2D532D;

src/gui/styles/light/lightstyle.qss

@@ -8,11 +8,16 @@ EntryPreviewWidget QLineEdit:disabled, EntryPreviewWidget QTextEdit:disabled {
     background-color: #EDEDED;
 }
 
-QGroupBox::title {
-    color: #4B7B19;
+QPushButton:default:hover {
+    /* Using slightly lighter shade from palette(highlight) */
+    background: #568821;
 }
 
 QToolTip {
     color: #F9F9F9;
     background-color: #4D7F1A;
 }
+
+QGroupBox::title {
+    color: #4B7B19;
+}