message: Style the snap drop indicator boxes
diff: * Copyright 2017 Simon Edwards <simon@simonzone.com>
  */
  +@import "extraterm-scrollbars";
  +
  #ID_TOP {
  position: relative;
  width: 100%;
  right: 0;
  }
  -$indicator_margin: 8px;
  +$indicator_margin: 16px;
  +$inner_shadow: 32px;
  #ID_DRAG_COVER {
  position: absolute;
  @@ -32,19 +35,22 @@ $indicator_margin: 8px;
  display: block;
  box-sizing: border-box;
  position: absolute;
  - border: 3px solid blue;
  +
  + background-color: rgba(255,255,255, 0.25);
  + box-shadow: 0px 0px #{$indicator_margin} 0px black, inset 0px 0px #{$inner_shadow} 0px white;
  + border-radius: 4px;
  }
  &.CLASS_DROP_TARGET_MIDDLE:before {
  left: #{$indicator_margin};
  - right: #{$indicator_margin};
  + right: #{$indicator_margin + $scrollbar-size + 2 * $scrollbar-pad};
  top: #{$indicator_margin};
  bottom: #{$indicator_margin};
  }
  &.CLASS_DROP_TARGET_NORTH:before, &.CLASS_DROP_TARGET_SOUTH:before {
  left: #{$indicator_margin};
  - right: #{$indicator_margin};
  + right: #{$indicator_margin + $scrollbar-size + 2 * $scrollbar-pad};
  }
  &.CLASS_DROP_TARGET_NORTH:before {
  @@ -64,7 +70,7 @@ $indicator_margin: 8px;
  &.CLASS_DROP_TARGET_EAST:before {
  left: 50%;
  - right: #{$indicator_margin};
  + right: #{$indicator_margin + $scrollbar-size + 2 * $scrollbar-pad};
  }
  &.CLASS_DROP_TARGET_WEST:before {
  