/* Layout Selector */
.xpress-editor{ position:relative; background:transparent;}
.xpress-editor #smart_content{ position:relative; clear:both; margin:0 0 10px 0; border:1px solid #c2c2c2; *zoom:1; z-index:5; background:#fff;}
.xpress-editor.black #smart_content {background:transparent;}
.xpress-editor #smart_footer{ position:relative; text-align:center; padding:10px 0;}

22번째 줄의 background:#fff; 를 수정하시면 되겠네요