Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Html.php
public function buildCSS($generateSurroundingHTML = true)
    {
        // Spreadsheet object known?
        if ($this->spreadsheet === null) {
            throw new WriterException('Internal Spreadsheet object not set to an instance of an object.');
        }

        // Cached?
        if ($this->cssStyles !== null) {
            return $this->cssStyles;
        }

        // Ensure that spans have been calculated
        if (!$this->spansAreCalculated) {
            $this->calculateSpans();
        }

        // Construct CSS
        $css = [];

        // Start styles
        if ($generateSurroundingHTML) {
            // html { }
            $css['html']['font-family'] = 'Calibri, Arial, Helvetica, sans-serif';
            $css['html']['font-size'] = '11pt';
            $css['html']['background-color'] = 'white';
        }

        // CSS for comments as found in LibreOffice
        $css['a.comment-indicator:hover + div.comment'] = [
            'background' => '#ffd',
            'position' => 'absolute',
            'display' => 'block',
            'border' => '1px solid black',
            'padding' => '0.5em',
        ];

        $css['a.comment-indicator'] = [
            'background' => 'red',
            'display' => 'inline-block',
            'border' => '1px solid black',
            'width' => '0.5em',
            'height' => '0.5em',
        ];

        $css['div.comment']['display'] = 'none';

        // table { }
        $css['table']['border-collapse'] = 'collapse';
        if (!$this->isPdf) {
            $css['table']['page-break-after'] = 'always';
        }

        // .gridlines td { }
        $css['.gridlines td']['border'] = '1px dotted black';
        $css['.gridlines th']['border'] = '1px dotted black';

        // .b {}
        $css['.b']['text-align'] = 'center'; // BOOL

        // .e {}
        $css['.e']['text-align'] = 'center'; // ERROR

        // .f {}
        $css['.f']['text-align'] = 'right'; // FORMULA

        // .inlineStr {}
        $css['.inlineStr']['text-align'] = 'left'; // INLINE

        // .n {}
        $css['.n']['text-align'] = 'right'; // NUMERIC

        // .s {}
        $css['.s']['text-align'] = 'left'; // STRING

        // Calculate cell style hashes
        foreach ($this->spreadsheet->getCellXfCollection() as $index => $style) {
            $css['td.style' . $index] = $this->createCSSStyle($style);
            $css['th.style' . $index] = $this->createCSSStyle($style);
        }

        // Fetch sheets
        $sheets = [];
        if ($this->sheetIndex === null) {
            $sheets = $this->spreadsheet->getAllSheets();
        } else {
            $sheets[] = $this->spreadsheet->getSheet($this->sheetIndex);
        }

        // Build styles per sheet
        foreach ($sheets as $sheet) {
            // Calculate hash code
            $sheetIndex = $sheet->getParent()->getIndex($sheet);

            // Build styles
            // Calculate column widths
            $sheet->calculateColumnWidths();

            // col elements, initialize
            $highestColumnIndex = Coordinate::columnIndexFromString($sheet->getHighestColumn()) - 1;
            $column = -1;
            while ($column++ < $highestColumnIndex) {
                $this->columnWidths[$sheetIndex][$column] = 42; // approximation
                $css['table.sheet' . $sheetIndex . ' col.col' . $column]['width'] = '42pt';
            }

            // col elements, loop through columnDimensions and set width
            foreach ($sheet->getColumnDimensions() as $columnDimension) {
                if (($width = SharedDrawing::cellDimensionToPixels($columnDimension->getWidth(), $this->defaultFont)) >= 0) {
                    $width = SharedDrawing::pixelsToPoints($width);
                    $column = Coordinate::columnIndexFromString($columnDimension->getColumnIndex()) - 1;
                    $this->columnWidths[$sheetIndex][$column] = $width;
                    $css['table.sheet' . $sheetIndex . ' col.col' . $column]['width'] = $width . 'pt';

                    if ($columnDimension->getVisible() === false) {
                        $css['table.sheet' . $sheetIndex . ' col.col' . $column]['visibility'] = 'collapse';
                        $css['table.sheet' . $sheetIndex . ' col.col' . $column]['*display'] = 'none'; // target IE6+7
                    }
                }
            }

            // Default row height
            $rowDimension = $sheet->getDefaultRowDimension();

            // table.sheetN tr { }
            $css['table.sheet' . $sheetIndex . ' tr'] = [];

            if ($rowDimension->getRowHeight() == -1) {
                $pt_height = SharedFont::getDefaultRowHeightByFont($this->spreadsheet->getDefaultStyle()->getFont());
            } else {
                $pt_height = $rowDimension->getRowHeight();
            }
            $css['table.sheet' . $sheetIndex . ' tr']['height'] = $pt_height . 'pt';
            if ($rowDimension->getVisible() === false) {
                $css['table.sheet' . $sheetIndex . ' tr']['display'] = 'none';
                $css['table.sheet' . $sheetIndex . ' tr']['visibility'] = 'hidden';
            }

            // Calculate row heights
            foreach ($sheet->getRowDimensions() as $rowDimension) {
                $row = $rowDimension->getRowIndex() - 1;

                // table.sheetN tr.rowYYYYYY { }
                $css['table.sheet' . $sheetIndex . ' tr.row' . $row] = [];

                if ($rowDimension->getRowHeight() == -1) {
                    $pt_height = SharedFont::getDefaultRowHeightByFont($this->spreadsheet->getDefaultStyle()->getFont());
                } else {
                    $pt_height = $rowDimension->getRowHeight();
                }
                $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['height'] = $pt_height . 'pt';
                if ($rowDimension->getVisible() === false) {
                    $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['display'] = 'none';
                    $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['visibility'] = 'hidden';
                }
            }
        }

        // Cache
        if ($this->cssStyles === null) {
            $this->cssStyles = $css;
        }

        // Return
        return $css;
    }
public function buildCSS($generateSurroundingHTML = true)
    {
        // Spreadsheet object known?
        if ($this->spreadsheet === null) {
            throw new WriterException('Internal Spreadsheet object not set to an instance of an object.');
        }

        // Cached?
        if ($this->cssStyles !== null) {
            return $this->cssStyles;
        }

        // Ensure that spans have been calculated
        if (!$this->spansAreCalculated) {
            $this->calculateSpans();
        }

        // Construct CSS
        $css = [];

        // Start styles
        if ($generateSurroundingHTML) {
            // html { }
            $css['html']['font-family'] = 'Calibri, Arial, Helvetica, sans-serif';
            $css['html']['font-size'] = '11pt';
            $css['html']['background-color'] = 'white';
        }

        // CSS for comments as found in LibreOffice
        $css['a.comment-indicator:hover + div.comment'] = [
            'background' => '#ffd',
            'position' => 'absolute',
            'display' => 'block',
            'border' => '1px solid black',
            'padding' => '0.5em',
        ];

        $css['a.comment-indicator'] = [
            'background' => 'red',
            'display' => 'inline-block',
            'border' => '1px solid black',
            'width' => '0.5em',
            'height' => '0.5em',
        ];

        $css['div.comment']['display'] = 'none';

        // table { }
        $css['table']['border-collapse'] = 'collapse';
        if (!$this->isPdf) {
            $css['table']['page-break-after'] = 'always';
        }

        // .gridlines td { }
        $css['.gridlines td']['border'] = '1px dotted black';
        $css['.gridlines th']['border'] = '1px dotted black';

        // .b {}
        $css['.b']['text-align'] = 'center'; // BOOL

        // .e {}
        $css['.e']['text-align'] = 'center'; // ERROR

        // .f {}
        $css['.f']['text-align'] = 'right'; // FORMULA

        // .inlineStr {}
        $css['.inlineStr']['text-align'] = 'left'; // INLINE

        // .n {}
        $css['.n']['text-align'] = 'right'; // NUMERIC

        // .s {}
        $css['.s']['text-align'] = 'left'; // STRING

        // Calculate cell style hashes
        foreach ($this->spreadsheet->getCellXfCollection() as $index => $style) {
            $css['td.style' . $index] = $this->createCSSStyle($style);
            $css['th.style' . $index] = $this->createCSSStyle($style);
        }

        // Fetch sheets
        $sheets = [];
        if ($this->sheetIndex === null) {
            $sheets = $this->spreadsheet->getAllSheets();
        } else {
            $sheets[] = $this->spreadsheet->getSheet($this->sheetIndex);
        }

        // Build styles per sheet
        foreach ($sheets as $sheet) {
            // Calculate hash code
            $sheetIndex = $sheet->getParent()->getIndex($sheet);

            // Build styles
            // Calculate column widths
            $sheet->calculateColumnWidths();

            // col elements, initialize
            $highestColumnIndex = Coordinate::columnIndexFromString($sheet->getHighestColumn()) - 1;
            $column = -1;
            while ($column++ < $highestColumnIndex) {
                $this->columnWidths[$sheetIndex][$column] = 42; // approximation
                $css['table.sheet' . $sheetIndex . ' col.col' . $column]['width'] = '42pt';
            }

            // col elements, loop through columnDimensions and set width
            foreach ($sheet->getColumnDimensions() as $columnDimension) {
                if (($width = SharedDrawing::cellDimensionToPixels($columnDimension->getWidth(), $this->defaultFont)) >= 0) {
                    $width = SharedDrawing::pixelsToPoints($width);
                    $column = Coordinate::columnIndexFromString($columnDimension->getColumnIndex()) - 1;
                    $this->columnWidths[$sheetIndex][$column] = $width;
                    $css['table.sheet' . $sheetIndex . ' col.col' . $column]['width'] = $width . 'pt';

                    if ($columnDimension->getVisible() === false) {
                        $css['table.sheet' . $sheetIndex . ' col.col' . $column]['visibility'] = 'collapse';
                        $css['table.sheet' . $sheetIndex . ' col.col' . $column]['*display'] = 'none'; // target IE6+7
                    }
                }
            }

            // Default row height
            $rowDimension = $sheet->getDefaultRowDimension();

            // table.sheetN tr { }
            $css['table.sheet' . $sheetIndex . ' tr'] = [];

            if ($rowDimension->getRowHeight() == -1) {
                $pt_height = SharedFont::getDefaultRowHeightByFont($this->spreadsheet->getDefaultStyle()->getFont());
            } else {
                $pt_height = $rowDimension->getRowHeight();
            }
            $css['table.sheet' . $sheetIndex . ' tr']['height'] = $pt_height . 'pt';
            if ($rowDimension->getVisible() === false) {
                $css['table.sheet' . $sheetIndex . ' tr']['display'] = 'none';
                $css['table.sheet' . $sheetIndex . ' tr']['visibility'] = 'hidden';
            }

            // Calculate row heights
            foreach ($sheet->getRowDimensions() as $rowDimension) {
                $row = $rowDimension->getRowIndex() - 1;

                // table.sheetN tr.rowYYYYYY { }
                $css['table.sheet' . $sheetIndex . ' tr.row' . $row] = [];

                if ($rowDimension->getRowHeight() == -1) {
                    $pt_height = SharedFont::getDefaultRowHeightByFont($this->spreadsheet->getDefaultStyle()->getFont());
                } else {
                    $pt_height = $rowDimension->getRowHeight();
                }
                $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['height'] = $pt_height . 'pt';
                if ($rowDimension->getVisible() === false) {
                    $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['display'] = 'none';
                    $css['table.sheet' . $sheetIndex . ' tr.row' . $row]['visibility'] = 'hidden';
                }
            }
        }

        // Cache
        if ($this->cssStyles === null) {
            $this->cssStyles = $css;
        }

        // Return
        return $css;
    }
Build CSS styles.

@param bool $generateSurroundingHTML Generate surrounding HTML style? (html { })

@throws WriterException

@return array