Mark.Huang @ 2015/08/19
CSS priority, you can refer to developer console style info, it shows priority, the topest is the highest priority, which html tag style should take precedence over CSS, multiple CSS depends on loading sequence. Seems last loaded will take effect, but mostly, they are computed result, effects may come from multiple CSS files
DIV, or in general, all html tags, except few one, are using same "rendering" principle, their position, depends on the type of positioning methods (fixed, absolute, relative, default etc), combined with other settings, it is not two dimension, but at least three dimensions, z-index controls which on the top. What I mean at least three dimensions, because you sometimes need to think about animation, which is time factor
why is childen element out of the region of its parent in common?how to make children always inside the region of its parent element?
A bit related