Userstyle to enforce a modern font stack on all websites

modern-font-stack.css

/* ==UserStyle==
@name           Modern Font Stack
@namespace      github.com/openstyles/stylus
@version        1.0.0
@license        MIT
@description    Replaces Segoe UI, Arial and Helvetica Neue with IBM Plex Sans on all websites
@author         Calinou
==/UserStyle== */

@-moz-document regexp(".*") {
@font-face {
  font-family: "Segoe UI";
  font-weight: 300;
  src: local("IBM Plex Sans Light");
}

@font-face {
  font-family: "Segoe UI";
  font-weight: 400;
  src: local("IBM Plex Sans Text");
}

@font-face {
  font-family: "Segoe UI";
  font-weight: 500;
  src: local("IBM Plex Sans Medium");
}

@font-face {
  font-family: "Segoe UI";
  font-weight: 600;
  src: local("IBM Plex Sans SemiBold");
}

@font-face {
  font-family: "Segoe UI";
  font-weight: 700;
  src: local("IBM Plex Sans Bold");
}

@font-face {
  font-family: "Arial";
  font-weight: 300;
  src: local("IBM Plex Sans Light");
}

@font-face {
  font-family: "Arial";
  font-weight: 400;
  src: local("IBM Plex Sans Text");
}

@font-face {
  font-family: "Arial";
  font-weight: 500;
  src: local("IBM Plex Sans Medium");
}

@font-face {
  font-family: "Arial";
  font-weight: 600;
  src: local("IBM Plex Sans SemiBold");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 700;
  src: local("IBM Plex Sans Bold");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 300;
  src: local("IBM Plex Sans Light");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 400;
  src: local("IBM Plex Sans Text");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 500;
  src: local("IBM Plex Sans Medium");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 600;
  src: local("IBM Plex Sans SemiBold");
}

@font-face {
  font-family: "Helvetica Neue";
  font-weight: 700;
  src: local("IBM Plex Sans Bold");
}
}