To change the font, you can add the @font-face in the CSS.

For example:

@font-face{
    font-family: Helvetica;
}

If you use another font like Roboto, you may need to add its source link:

@font-face{
    font-family: Helvetica;
    src: 'source link here',
}

Or you may just set in the text itself like this:

span {
  font-family: helvetica;
}

p {
  font-family: serif;
}

<span>Helvetica</span> <br>
<p>Serif</p>

In that repository, the font style is defined in:

Go to your CSS folder and to the fonts.css

/* @font-face */ 

@font-face{
font-family: "Roboto";
src: '../fonts/Roboto/Roboto-Regular.ttf';
}

then change this to any font you want. just download a new font pack online and replace the font folder. Then route that new font folder this css.

i.e

/* @font-face */ 

@font-face{
font-family: "super-cool";
src: '../fonts/super-cool/super-cool-Regular.ttf';
}