Qt embedded CEF,window transparent,page doesn't rendering

[powerwheel]

I use CEF3 in Qt, when set main window broderless and transparent , the web page can't rendering;
before set:

after:

setWindowFlags(Qt::Dialog | Qt::FramelessWindowHint | Qt::WindowMinimizeButtonHint | Qt::WindowSystemMenuHint);
setAttribute(Qt::WA_TranslucentBackground);

can someone help me?
thanks