Vendor/phpspreadsheet/phpoffice/phpspreadsheet/src/PhpSpreadsheet/Writer/Html.php
private function mapBorderStyle($borderStyle)
    {
        switch ($borderStyle) {
            case Border::BORDER_NONE:
                return 'none';
            case Border::BORDER_DASHDOT:
                return '1px dashed';
            case Border::BORDER_DASHDOTDOT:
                return '1px dotted';
            case Border::BORDER_DASHED:
                return '1px dashed';
            case Border::BORDER_DOTTED:
                return '1px dotted';
            case Border::BORDER_DOUBLE:
                return '3px double';
            case Border::BORDER_HAIR:
                return '1px solid';
            case Border::BORDER_MEDIUM:
                return '2px solid';
            case Border::BORDER_MEDIUMDASHDOT:
                return '2px dashed';
            case Border::BORDER_MEDIUMDASHDOTDOT:
                return '2px dotted';
            case Border::BORDER_MEDIUMDASHED:
                return '2px dashed';
            case Border::BORDER_SLANTDASHDOT:
                return '2px dashed';
            case Border::BORDER_THICK:
                return '3px solid';
            case Border::BORDER_THIN:
                return '1px solid';
            default:
                // map others to thin
                return '1px solid';
        }
    }
private function mapBorderStyle($borderStyle)
    {
        switch ($borderStyle) {
            case Border::BORDER_NONE:
                return 'none';
            case Border::BORDER_DASHDOT:
                return '1px dashed';
            case Border::BORDER_DASHDOTDOT:
                return '1px dotted';
            case Border::BORDER_DASHED:
                return '1px dashed';
            case Border::BORDER_DOTTED:
                return '1px dotted';
            case Border::BORDER_DOUBLE:
                return '3px double';
            case Border::BORDER_HAIR:
                return '1px solid';
            case Border::BORDER_MEDIUM:
                return '2px solid';
            case Border::BORDER_MEDIUMDASHDOT:
                return '2px dashed';
            case Border::BORDER_MEDIUMDASHDOTDOT:
                return '2px dotted';
            case Border::BORDER_MEDIUMDASHED:
                return '2px dashed';
            case Border::BORDER_SLANTDASHDOT:
                return '2px dashed';
            case Border::BORDER_THICK:
                return '3px solid';
            case Border::BORDER_THIN:
                return '1px solid';
            default:
                // map others to thin
                return '1px solid';
        }
    }
Map border style.

@param int $borderStyle Sheet index

@return string