Check icon in contact form

Hello,
With the updates theme + Ocean Extra, the icon “check” does not appear anymore when clicking into the box. As you can see, a square shows instead.
I have found this CSS on the net to solve the problem :
input[type=checkbox]:checked:before { font-family: ‘Font Awesome 5 Free’;}
But it does not work on all sites.

Could you please tell me how to fix this issue.
Thanks a lot

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