I highly advice agains’t this.
Your website requires this stylesheet to look the way it does by having it load later you are only slowing down the time it takes for the user to get a visually good looking website its not going to give any speed improvements.
however to answer your question
in the href you’d put your stylesheet asset url
If you want to focus on speed improvements instead try to split up your styles.css into a global css (which would be used to store the style rules that apply to every page) and then to make multiple small css files that you ONLY load onto the page where they are specificly made for.
This will greatly improve your site speed by having your users only load css thats important for them. and the webbrowser only having to calculate and process important css