You would overlay the same way - there is no difference from JSP other than you are using Sightly code.
Move to /apps and change the Sightly code.
We have a lot of articles on using Sightly. See this reference:
https://helpx.adobe.com/experience-manager/using/creating-sightly-component.html
See the beginning of this article. You will see links to other Sightly content and Ask the AEM Community Expert sessions on Sightly.
Hope this helps.