protected @Nullable Border createContentPaneBorder() {
    if (getStyle() == DialogStyle.COMPACT) {
      if (/*(SystemInfoRt.isMac && Registry.is("ide.mac.transparentTitleBarAppearance", true)) ||*/
          (SystemInfoRt.isWindows && SystemInfo.isJetBrainsJvm)) {
        return JBUI.Borders.customLineTop(JBUI.CurrentTheme.CustomFrameDecorations.separatorForeground());
      }
      return JBUI.Borders.empty();
    }
    return createDefaultBorder();
  }
protected @Nullable Border createContentPaneBorder()