.ow_box_empty {
background-color: #262c3a;
position: relative;
padding: 10px;
/* border: 1px solid #1e2432; */
-webkit-box-shadow: 0 1px 3px rgba(0, 0, 0, .3), inset 0 1px 1px rgba(255, 255, 255, .2);
-moz-box-shadow: 0 1px 3px rgba(0, 0, 0, .3), inset 0 1px 1px rgba(255, 255, 255, .2);
box-shadow: 0 1px 3px rgba(0, 0, 0, .3), inset 0 1px 1px rgba(255, 255, 255, .2);
}
on line 2136 of the default bace.css file
you need to remove background-color or apply your color and remove border or apply your color. Don't forget above dev mode.