Кнопка «Наверх»

<div class="fixed bottom-4 right-4">
  <a href="#" class="bg-blue-500 text-white p-3 rounded-full shadow-md transition-opacity duration-300 opacity-0 group-hover:opacity-100 dark:bg-blue-700 dark:text-gray-200">
    <svg class="w-6 h-6" fill="none" stroke="currentColor" viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M5 10l7-7m0 0l7 7m-7-7v18"></path></svg>
  </a>
</div>

<style>
  /* This simple example uses CSS for smooth scrolling. For a production site, you might use a small amount of JavaScript for better compatibility and control over the scroll behavior and when the button appears. */
  html {
    scroll-behavior: smooth;
  }

  /* Basic example to show/hide the button based on scroll position. 
     A robust solution would involve JavaScript Intersection Observer or scroll events. */
  body:before {
    content: "";
    height: 200vh; /* Simulate a long page */
    display: block;
  }

  .group-hover\:opacity-100:hover + .fixed a {
      opacity: 1; /* This part is flawed for demonstrating scroll-based visibility without JS */
  }

  /* A better approach for scroll-based visibility would require JavaScript */
  .fixed a {
      /* Initially hidden, JS would make it visible on scroll */
      opacity: 0;
      transition: opacity 0.3s ease-in-out;
  }


</style>