code: public function allBorders(Spreadsheet $spreadsheet)
      {
          // Get an array of unique borders
          $aBorders = [];
          $aStyles = $this->allStyles($spreadsheet);
  
          /** @var \PhpOffice\PhpSpreadsheet\Style\Style $style */
          foreach ($aStyles as $style) {
              if (!isset($aBorders[$style->getBorders()->getHashCode()])) {
                  $aBorders[$style->getBorders()->getHashCode()] = $style->getBorders();
              }
          }
  
          return $aBorders;
      }
docs: Get an array of all borders.
  
  @param Spreadsheet $spreadsheet
  
  @return Borders[] All borders in PhpSpreadsheet