The problem is the width you set on the .el
elements, change this width to 100% and you gap will be removed.
See this FIDDLE
HTML :
<div id="cols">
<div>ELEMENT</div>
<div>ELEMENT</div>
<div>ELEMENT</div>
...
</div>
CSS :
#cols {
height: 100%;
-webkit-column-width: 25em;
-moz-column-width: 25em;
-ms-column-width: 25em;
-o-column-width: 25em;
column-width: 25em;
-webkit-column-gap: 0;
-moz-column-gap: 0;
-ms-column-gap: 0;
-o-column-gap: 0;
column-gap: 0;
}
#cols > div{
background:gold;
height:50px;
margin:5px 0;
display:inline-block;
width:100%; /*<-- this line */
}