[Vuejs]-In my vue project i have tried using simple bootstrap along with sass and pug unable to use bootstrap. It's giving me error

I think I might be late with my answer, but I will answer, anyway, because I had the same issue today.

The idea is that package.json is storing your PostCSS configuration. So, you need to at least add PostCSS options key if it wasn’t set yet:

"postcss": {
    "options": {},
    "plugins": {
        "autoprefixer": {}
    }
}

UPD: by the way, I think this type of error appears with external CSS only and pug might not be related.