superset-frontend/packages/superset-frontend/src/dashboard/stylesheets/components/column.less

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
.grid-column {
  width: 100%;
  position: relative;
}

/* gutters between elements in a column */
.grid-column > :not(:only-child):not(.hover-menu):not(:last-child) {
  margin-bottom: 16px;
}

.dashboard--editing {
  .grid-column:after {
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    z-index: @z-index-chart;
    pointer-events: none;
    border: 1px dashed @gray-light;
  }

  .resizable-container.resizable-container--resizing:hover > .grid-column:after,
  .hover-menu:hover + .grid-column:after {
    border: 1px dashed @indicator-color;
    z-index: @z-index-chart--dragging;
  }
}

.grid-column--empty {
  min-height: 100px;

  &:before {
    content: 'Empty column';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    color: @gray-light;
  }
}