Change default font in vuetify is not working (vue-cli 3) [Vuetify 1.X]

So I just took a quick and fresh glance back to this, at the end it was something silly, if a project is created with vue-cli 3 (either custom choices or default), then obviously in the component App.vue I had to take out font-family from the style section as it overwrites the CSS:

#app {
  font-family: 'Avenir', Helvetica, Arial, sans-serif; /* this was it */
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
}

EDIT:
It's possible that some styles are broken when importing styles from main.styl:
https://github.com/vuetifyjs/vuetify/issues/3583

---

Does everything load, do you get any errors?

It seems it should work, unless perhaps you have some typos somewhere, or incorrect paths?
For example stylus should be styles in your @require '~vuetify/src/stylus/main.styl'.

do I have to do also vue add stylus-loader?

It should already be added for you.

If you did not select specific CSS preprocessor (i.e. stylus) during vue-cli installation, then you need to add it manually
npm i -S stylus stylus-loader

module: {
  rules: [
    {
      test: /\.styl$/,
      loader: ['style-loader', 'css-loader', 'stylus-loader']
    }
  ]
}