CSS Positioning two images in div -

CSS Positioning two images in div -

i'm trying set images in style: one on top , other below this. wrong , in result images 1 under other. here is jsfiddle.

the sec image hidden overflow:hidden in slider class.

question:

where create mistake? i'm sure there easy solution lost time , can't find it.

p.s. if possible i'm looking solution css changes only.

change css images this:

img{ display:block; }

that trick.

edit after comments:

img{ position: absolute; z-index: -1; top: 0px; left:0; }

that staples images on each other in top left corner.

css image position