Back-to-Top Button

(function () {
  'use strict';

  document.addEventListener('DOMContentLoaded', function () {
    var btn = document.createElement('button');
    btn.id = 'back-to-top';
    btn.setAttribute('aria-label', 'Back to top');
    btn.innerHTML = '⇧';
    btn.style.cssText = [
      'position:fixed',
      'bottom:2rem',
      'right:2rem',
      'width:44px',
      'height:44px',
      'border-radius:50%',
      'background:#3b82f6',
      'color:#fff',
      'border:none',
      'font-size:1.5rem',
      'cursor:pointer',
      'opacity:0',
      'transition:opacity 0.3s',
      'z-index:999',
      'pointer-events:none'
    ].join(';');
    document.body.appendChild(btn);

    window.addEventListener('scroll', function () {
      if (window.scrollY > 400) {
        btn.style.opacity = '1';
        btn.style.pointerEvents = 'auto';
      } else {
        btn.style.opacity = '0';
        btn.style.pointerEvents = 'none';
      }
    }, { passive: true });

    btn.addEventListener('click', function () {
      window.scrollTo({ top: 0, behavior: 'smooth' });
    });
  });
})();