bPopup is a lightweight jQuery modal popup plugin (only 1.34KB gzipped). It doesn't create or style your popup but provides you with all the logic like centering, modal overlay, events and more. It gives you a lot of opportunities to customize so it will fit your needs.
Studying the code, I think I saw that starting vPos for a slideDown-effected popup was its ending vPos minus its height. But if popup height is quite small and/or window height quite big, popup's bottom is visible when starting sliding down effect and then, effect is not a full sliding down (i.e. from out-of-screen to screen) anymore.
But maybe this is a normal behaviour for you.
In any case many many thanks for this beautiful tool.
Studying the code, I think I saw that starting vPos for a slideDown-effected popup was its ending vPos minus its height. But if popup height is quite small and/or window height quite big, popup's bottom is visible when starting sliding down effect and then, effect is not a full sliding down (i.e. from out-of-screen to screen) anymore. But maybe this is a normal behaviour for you. In any case many many thanks for this beautiful tool.