HomeWindow: fix background white flash while switching to onroad (#21695)

selfdrive/ui/qt/home.cc

@@ -39,6 +39,7 @@ HomeWindow::HomeWindow(QWidget* parent) : QWidget(parent) {
     showDriverView(false);
   });
   slayout->addWidget(driver_view);
+  setAttribute(Qt::WA_NoSystemBackground);
 }
 
 void HomeWindow::showSidebar(bool show) {
@@ -46,12 +47,12 @@ void HomeWindow::showSidebar(bool show) {
 }
 
 void HomeWindow::offroadTransition(bool offroad) {
+  sidebar->setVisible(offroad);
   if (offroad) {
     slayout->setCurrentWidget(home);
   } else {
     slayout->setCurrentWidget(onroad);
   }
-  sidebar->setVisible(offroad);
   emit offroadTransitionSignal(offroad);
 }
 

selfdrive/ui/qt/window.cc

@@ -59,6 +59,7 @@ MainWindow::MainWindow(QWidget *parent) : QWidget(parent) {
       outline: none;
     }
   )");
+  setAttribute(Qt::WA_NoSystemBackground);
 }
 
 void MainWindow::openSettings() {