ntp_card_background missing from advanced

[MartijnOud]

Hi! Under the advanced settings there are options for 'New Tab Background Color' (ntp_background) and 'New Tab Text' (ntp_text) but it seems the related ntp_card_background is missing.

[Rob--W]

To fix this we have to add an entry for ntp_card_background at

FirefoxColor/src/lib/constants.js

Lines 42 to 43 in 2738144

	ntp_background: "New Tab Background Color",
	ntp_text: "New Tab Text",

This property was added in 2021 https://bugzilla.mozilla.org/show_bug.cgi?id=1727333

Unfortunately the site has not been updated for a while, even the changes from #819 (2019) are not included in the currently deployed site.