code: public TableCellStyle addChildCellStyle(final TableCellStyle style, final DataStyle dataStyle) {
          final ChildCellStyle childKey = new ChildCellStyle(style, dataStyle);
          TableCellStyle anonymousStyle = this.anonymousStyleByChildCellStyle.get(childKey);
          if (anonymousStyle == null) {
              this.addDataStyle(dataStyle);
              if (!style.hasParent()) { // here, the style may already be a child style
                  this.addContentFontFaceContainerStyle(style);
              }
              final String name = style.getRealName() + "-_-" + dataStyle.getName();
              final TableCellStyleBuilder anonymousStyleBuilder = TableCellStyle.builder(name)
                      .parentCellStyle(style).dataStyle(dataStyle);
              if (dataStyle.isHidden()) {
                  anonymousStyleBuilder.hidden();
              }
              anonymousStyle = anonymousStyleBuilder.build();
              this.addContentFontFaceContainerStyle(anonymousStyle);
              this.anonymousStyleByChildCellStyle.put(childKey, anonymousStyle);
          }
          return anonymousStyle;
      }
docs: Add a child style that mixes the cell style with a data style to the container
  
  @param style     the cell style
  @param dataStyle the data style
  @return the mixed cell style