title: Next.js use of _app.js and _document.js
body: <p>I currently use <code>_document.js</code> to inject css into my Next.js app and I would like to start using <code>_app.js</code> to help inject data into pages. </p>
  
  <p>Was wondering if it possible to use _document and _app in tandem or should we only use one or the other?</p>