code: public function generateStyles($generateSurroundingHTML = true)
      {
          // Spreadsheet object known?
          if ($this->spreadsheet === null) {
              throw new WriterException('Internal Spreadsheet object not set to an instance of an object.');
          }
  
          // Build CSS
          $css = $this->buildCSS($generateSurroundingHTML);
  
          // Construct HTML
          $html = '';
  
          // Start styles
          if ($generateSurroundingHTML) {
              $html .= '    <style type="text/css">' . PHP_EOL;
              $html .= '      html { ' . $this->assembleCSS($css['html']) . ' }' . PHP_EOL;
          }
  
          // Write all other styles
          foreach ($css as $styleName => $styleDefinition) {
              if ($styleName != 'html') {
                  $html .= '      ' . $styleName . ' { ' . $this->assembleCSS($styleDefinition) . ' }' . PHP_EOL;
              }
          }
  
          // End styles
          if ($generateSurroundingHTML) {
              $html .= '    </style>' . PHP_EOL;
          }
  
          // Return
          return $html;
      }
docs: Generate CSS styles.
  
  @param bool $generateSurroundingHTML Generate surrounding HTML tags? (&lt;style&gt; and &lt;/style&gt;)
  
  @throws WriterException
  
  @return string