code: public function allConditionalStyles(Spreadsheet $spreadsheet)
      {
          // Get an array of all styles
          $aStyles = [];
  
          $sheetCount = $spreadsheet->getSheetCount();
          for ($i = 0; $i < $sheetCount; ++$i) {
              foreach ($spreadsheet->getSheet($i)->getConditionalStylesCollection() as $conditionalStyles) {
                  foreach ($conditionalStyles as $conditionalStyle) {
                      $aStyles[] = $conditionalStyle;
                  }
              }
          }
  
          return $aStyles;
      }
docs: Get an array of all conditional styles.
  
  @param Spreadsheet $spreadsheet
  
  @return Conditional[] All conditional styles in PhpSpreadsheet