docs: function renderBackground(group, bg, useUpperLabel) {
          // For tooltip.
          bg.dataIndex = thisNode.dataIndex;
          bg.seriesIndex = seriesModel.seriesIndex;
  
          bg.setShape({x: 0, y: 0, width: thisWidth, height: thisHeight});
          var visualBorderColor = thisNode.getVisual('borderColor', true);
          var emphasisBorderColor = itemStyleEmphasisModel.get('borderColor');
  
          updateStyle(bg, function () {
              var normalStyle = getItemStyleNormal(itemStyleNormalModel);
              normalStyle.fill = visualBorderColor;
              var emphasisStyle = getItemStyleEmphasis(itemStyleEmphasisModel);
              emphasisStyle.fill = emphasisBorderColor;
  
              if (useUpperLabel) {
                  var upperLabelWidth = thisWidth - 2 * borderWidth;
  
                  prepareText(
                      normalStyle, emphasisStyle, visualBorderColor, upperLabelWidth, upperHeight,
                      {x: borderWidth, y: 0, width: upperLabelWidth, height: upperHeight}
                  );
              }
              // For old bg.
              else {
                  normalStyle.text = emphasisStyle.text = null;
              }
  
              bg.setStyle(normalStyle);
              graphic.setHoverStyle(bg, emphasisStyle);
          });
  
          group.add(bg);
      }