Use the background
shorthand to position the element and change the display to inline-block
as opposed to than floating it.
.closeIcon {
width:16px;
height:16px;
margin:2px -10px 0 4px;
display:inline-block;
background: url('http://s21.postimg.org/jam8gpcr7/themes_windows_global_icons_close.png') -1px 4px / 64px 16px no-repeat;
}
The floating element was the culprit.