Why do some font awesome icons look like squares?

Question

Character encoding

I'm editing the template. Font awesome is connected, some icons are displayed correctly, while others are in the form of squares or hieroglyphs.
Styles are written like this:

.fa-html5:before {
 	content: "\f13b"
 }

 .fa-css3:before {
 	content: "\f13c"
 }

.fa-sass:before {
       	content: "\f41e"
}

In html like this

<i class="fa fa-html5 fa-5x"></i>
<i class="fa fa-css3 fa-5x"></i>
<i class="fa fa-sass fa-5x"></i>

Everything seems to be correct, but the first two icons are normally visible, and the third is a square .. What could be the matter?