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• structure or content layer

  • HTML structure can consist of text or images and it includes the hyperlinks that visitors will use to navigate around that web site. 
• style or presentation layer

  • CSS (Cascading Style Sheets).
  •  style layer can also include Media Queries that can change a site's display based on different screen sizes and devices.
• behavior layer

  • the behavior level would be the JavaScript interactions on the page.