code: public boolean addStylesFontFaceContainerStyle(final FontFaceContainerStyle ffcStyle) {
          final FontFace fontFace = ffcStyle.getFontFace();
          if (fontFace != null) {
              this.fontFaces.add(fontFace);
          }
          return this.addStylesStyle(ffcStyle);
      }
docs: Add a cell style to the content container and register the font face
  @param ffcStyle the cell style or the text style
  @return true if the style was created or updated