The safe area specifies where information, that is important to the user, should be displayed. It's defined through margins from each side which should not be used for displaying important information, as it may not be visible to the user. The panel is still expected to draw in these margins, though.
In addition to the margins, there is padding within the safe area that is visible to the user, but should still not be used for important information. To calculate the distance of one side to where it is safe to put important information, paddingPx should be added to the margin of that side.