Mailspring/app/static/resizable.less

@resizableBorder: 1px solid #bbb;

.resizable {
  position: relative;
}

.resizable .resizeBar {
  box-sizing: border-box;
  display: block;
  position: absolute;

  &.top, &.bottom {
    height: 5px;
    width: 100%;
    cursor: ns-resize;
  }

  &.left, &.right {
    width: 5px;
    height: 100%;
    cursor: ew-resize;
  }

  &.top {
    border-top: @resizableBorder;
    top: 0;
  }

  &.bottom {
    border-bottom: @resizableBorder;
    bottom: 0;
  }

  &.left {
    border-left: @resizableBorder;
    left: 0;
  }

  &.right {
    border-right: @resizableBorder;
    right: 0;
  }
}