Invalid / Unknown character in CSS in external need links

[Stausssi]

Hi, I've stumbled upon a character error in external need links:

sphinx-needs/sphinx_needs/css/common/need_links.css

Lines 13 to 17 in 650cc3d

	a.external_link:after {
	content: "🡽"
	/* Same, but with none breaking space (&nbsp not supported in content!)*/
	/*content: "\00a0\00a0🡽"*/
	}

which unfortunately also renders in the HTML output: