In your Vue Project, add your favourite CSS Framework vis npm.

npm install tachyons --save-dev

In main.js add:

import 'tachyons/css/tachyons.min.css' 
// no need for ./../node_modules/ prefix

Adding a Static CSS File

Add style.css to /public/:

In /public/index.html reference the Style Sheet:

<link rel="stylesheet" type="text/css" href="style.css">