code: public CSSStyleSheetImpl merge() {
          final CSSStyleSheetImpl merged = new CSSStyleSheetImpl();
          final CSSRuleListImpl cssRuleList = new CSSRuleListImpl();
          final Iterator<CSSStyleSheetImpl> it = getCSSStyleSheets().iterator();
          while (it.hasNext()) {
              final CSSStyleSheetImpl cssStyleSheet = it.next();
              final CSSMediaRuleImpl cssMediaRule = new CSSMediaRuleImpl(merged, null, cssStyleSheet.getMedia());
              cssMediaRule.setRuleList(cssStyleSheet.getCssRules());
              cssRuleList.add(cssMediaRule);
          }
          merged.setCssRules(cssRuleList);
          merged.setMediaText("all");
          return merged;
      }
docs: Merges all StyleSheets in this list into one.
  
  @return the new (merged) StyleSheet