Styling <td> elements with an HSL border-color causes an exception in some circumstances

[theodore-gregor]

Guidelines

• I understand that if I fail to provide all required details, this issue may be closed without review.

Description of the bug

When trying to render a <td> element styled with an HSL border-color and a border-style of either groove, ridge, inset, or outset, I get the following exception:

Invalid color input, binary color string expected

mPDF version

8.1.5

PHP Version and environment (server type, cli provider etc., enclosing libraries and their respective versions)

8.1.6 served via Apache 2.4.57

Reproducible PHP+CSS+HTML snippet suffering by the error

$mpdf = new \Mpdf\Mpdf();
$mpdf->WriteHTML('<table><tr><td style="border-width:1px;border-color:hsl(0, 0%, 0%);border-style:groove">Testing</td></tr></table>');
$mpdf->Output();