add scss support in Vue 3 code example

Example 1: importing scss into vue component

<style lang="scss">
    @import 'sass/app.scss';
    html, body{
        margin: 0px;
        padding: 0px;
        background-color: $secondary-color;
    }
</style>

Example 2: vue add sass

<!--
# Run this command in the root dir of your vue project:
npm i sass-loader node-sass style-loader
-->

<!-- And later in your vue component -->
<style lang="sass">
/* Your sass code */
</style>