chatgui: remove universal black background from video window (fix black boxes around controls)

tools/chatgui/src/videoplayer_window.cpp

@@ -79,7 +79,6 @@ VideoPlayerWindow::VideoPlayerWindow(QWidget* parent)
     setWindowTitle(QStringLiteral("Video"));
     setFocusPolicy(Qt::StrongFocus);
     setMouseTracking(true);
-    setStyleSheet("background-color: black;");
 
     m_engine = new VideoPlayerEngine(this);