Buick LaCrosse can't close the skylight, and it may be opened in the always-on mode. Generally, there will be a button next to the light at the top of the cab, and there are three modes on the button, namely, always-on mode, door-opening mode and closed mode.
Usually, it will be set to the door mode, which will automatically light up when the Buick LaCrosse door is opened and automatically close when the door is closed. If the button is set to ON, the light will stay on and need to be turned off manually.