Add new option "Ignore system colors" for dark themes.

It will set default background of html element to white.
However, this may break some sites, so let's just make this
optional.

src/lib/app/mainapplication.cpp

@@ -399,8 +399,10 @@ void MainApplication::loadSettings()
     m_websettings->setAttribute(QWebSettings::JavascriptCanCloseWindows, settings.value("allowJavaScriptCloseWindow", false).toBool());
 #endif
 
+    const QUrl &styleSheet = userStyleSheet(settings.value("userStyleSheet", QString()).toString(),
+                                            settings.value("ignoreSystemColors", false).toBool());
+    m_websettings->setUserStyleSheetUrl(styleSheet);
     setWheelScrollLines(settings.value("wheelScrollLines", wheelScrollLines()).toInt());
-    m_websettings->setUserStyleSheetUrl(userStyleSheet(settings.value("userStyleSheet", QString()).toString()));
     settings.endGroup();
 
     settings.beginGroup("Browser-Fonts");
@@ -834,7 +836,8 @@ void MainApplication::reloadUserStyleSheet()
 {
     Settings settings;
     settings.beginGroup("Web-Browser-Settings");
-    m_websettings->setUserStyleSheetUrl(userStyleSheet(settings.value("userStyleSheet", QString()).toString()));
+    m_websettings->setUserStyleSheetUrl(userStyleSheet(settings.value("userStyleSheet", QString()).toString(),
+                                        settings.value("ignoreSystemColors", false).toBool()));
     settings.endGroup();
 }
 
@@ -880,11 +883,18 @@ RegisterQAppAssociation* MainApplication::associationManager()
 }
 #endif
 
-QUrl MainApplication::userStyleSheet(const QString &filePath) const
+QUrl MainApplication::userStyleSheet(const QString &filePath, bool ignoreSystemColors) const
 {
+    QString userStyle;
+
+    if (ignoreSystemColors) {
         // Set default white background for all sites
         // Fixes issue with dark themes when sites don't set background
-    QString userStyle = "html{background-color:white;}";
+        // But it also brings issues with background of iframes that assumes
+        // background will by default will be transparent
+        userStyle += "html{background-color:white;}";
+    }
+
     userStyle += AdBlockManager::instance()->elementHidingRules() + "{ display:none !important;}";
 
     QFile file(filePath);

src/lib/app/mainapplication.h

@@ -148,7 +148,7 @@ private:
     void translateApp();
     void restoreOtherWindows();
 
-    QUrl userStyleSheet(const QString &filePath) const;
+    QUrl userStyleSheet(const QString &filePath, bool ignoreSystemColors) const;
 
     CookieManager* m_cookiemanager;
     BrowsingLibrary* m_browsingLibrary;

src/lib/preferences/preferences.cpp

@@ -253,6 +253,7 @@ Preferences::Preferences(QupZilla* mainClass, QWidget* parent)
     ui->wheelScroll->setValue(settings.value("wheelScrollLines", qApp->wheelScrollLines()).toInt());
     ui->defaultZoom->setValue(settings.value("DefaultZoom", 100).toInt());
     ui->xssAuditing->setChecked(settings.value("XSSAuditing", false).toBool());
+    ui->ignoreSystemColors->setChecked(settings.value("ignoreSystemColors", false).toBool());
 
     //Cache
     ui->pagesInCache->setValue(settings.value("maximumCachedPages", 3).toInt());
@@ -898,6 +899,7 @@ void Preferences::saveSettings()
     settings.setValue("LoadTabsOnActivation", ui->dontLoadTabsUntilSelected->isChecked());
     settings.setValue("DefaultZoom", ui->defaultZoom->value());
     settings.setValue("XSSAuditing", ui->xssAuditing->isChecked());
+    settings.setValue("ignoreSystemColors", ui->ignoreSystemColors->isChecked());
 #ifdef Q_OS_WIN
     settings.setValue("CheckDefaultBrowser", ui->checkDefaultBrowser->isChecked());
 #endif

src/lib/preferences/preferences.ui

@@ -596,11 +596,11 @@
            <item row="9" column="0" colspan="2">
             <widget class="QLabel" name="label_7">
              <property name="text">
-              <string>&lt;b&gt;Background&lt;b/&gt;</string>
+              <string>&lt;b&gt;Colors&lt;b/&gt;</string>
              </property>
             </widget>
            </item>
-           <item row="11" column="1">
+           <item row="12" column="1">
             <spacer name="verticalSpacer_12">
              <property name="orientation">
               <enum>Qt::Vertical</enum>
@@ -641,6 +641,13 @@
              </property>
             </widget>
            </item>
+           <item row="11" column="1">
+            <widget class="QCheckBox" name="ignoreSystemColors">
+             <property name="text">
+              <string>Ignore system colors (for dark themes)</string>
+             </property>
+            </widget>
+           </item>
           </layout>
          </widget>
         </widget>