thanks for your answer.
I add display:none in submenu and display:inline when hovered on parent li. It solved a problem that it is visible when mouse is on submenu area.
however, there is another problem that it disappears when mouse is moved from parent list to submenu. Additionally, I added transition in submenu but it doesn’t work.
here’s edited code https://codepen.io/flsqja/pen/gyQqLe
thanks for you help