ryanoasis/nerd-fonts

Hey there! 👋
First of all: I am very new to CSS (to be honest, at the moment I am at the level of "playing with Firefox developer tool and see what happens").
I just tried to use some icons from nerdfonts' cheat sheet for a GitLab page. I use the lanyon theme from jekyll (https://jekyll-themes.com/lanyon/).
To use nerdfonts' icons, I've written

<link rel="stylesheet" href="https://github.com/ryanoasis/nerd-fonts/blob/master/css/nerd-fonts-generated.css">

and

<script src="https://github.com/ryanoasis/nerd-fonts/blob/master/css/nerd-fonts-generated.css">

in my head.html file (when I used <link rel=..., I put <script src=... in comments with <!-- ... -- > and vice versa to test both options).

But when I use

<i class="NERDFONTSYMBOLCODE"></i>

nothing happens 😢

I even saved a nerdfonts.css file in my css directory with following code:

 font-family:'NerdFontsSymbols Nerd Font';
 src:url("../fonts/Symbols-2048-em Nerd Font Complete.woff2") format("woff2");
 font-weight:400;
 font-style:normal
}
.nf,
.nerd-font,
.nerd-fonts {
 font-family:'NerdFontsSymbols Nerd Font';
 speak:none;
 font-style:normal;
 font-weight:400;
 font-variant:normal;
 text-transform:none;
 line-height:1;
 -webkit-font-smoothing:antialiased;
 -moz-osx-font-smoothing:grayscale
}
.nf-custom-c:before {
 content:"\e61e"
...

But even this didn't worked 😕
Does someone of you might have an idea ?

It would work with fontawesome.
I created an account at https://fontawesome.com so that I got a code line like

<script src="https://kit.fontawesome.com/..." ...></script>

but there are only very few options for a free account (why I want to use nerdfonts).