Please enter valid username CSS rules.

[CtrlV]

Im having problem in adding fontawesome icon after the username of every user in a group.

Based on my understanding on https://xenforo.com/community/resources/font-awesome-icons-2-3.9562/

code less should be like this
Code:

&:after{
    .m-faContent(@fa-var-icon-name);
}

but it always show error cant save.
Oops! We ran into some problems.
Please enter valid username CSS rules.
Please enter valid username CSS rules.

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