remove black frame from ulauncher

ulauncher.md

Extended white theme:

.app {
   box-shadow: 0 0 5px @window_shadow;
   background-color: @window_bg;
   border: 1px solid @window_border_color;
   border-radius: 4px;
   margin: -20px; /*override black area when window effect is disabled*/
}

Extended dark theme:

   background-color: @window_bg;
   border-color: @window_border_color;
   margin: -20px; /*override black area when window effect is disabled*/
}