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<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <title>Mobile-First Design Example</title> <link rel="stylesheet" href="style.css"> </head> <body> <header> <h1>Mobile-First Design</h1> </header> <main> <section class="content"> <p>This is a mobile-first design example.</p> </section> </main> </body> </html>