<button class="radikalwp-nav-backtop" data-backtop aria-label="بازگشت به بالای صفحه"><span class="radikalwp-nav-backtop-arrow">↑<//span><//button>

.radikalwp-nav-backtop {
  position: fixed;
  bottom: 26px;
  left: 26px;
  z-index: 60;
  width: 48px;
  height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 19px;
  color: #4f46e5;
  background: rgba(255, 255, 255, .8);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border: 1px solid #e0e7ff;
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 10px 26px rgba(79, 70, 229, .18);
  opacity: 0;
  transform: translateY(14px);
  pointer-events: none;
  transition: opacity .35s ease, transform .35s ease, background .3s ease;
}
.radikalwp-nav-backtop.is-visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}
.radikalwp-nav-backtop:hover { background: #fff; }
.radikalwp-nav-backtop:active { transform: scale(.92); }

// نمایش بعد از ۴۰۰ پیکسل اسکرول + پرش نرم به بالا
document.querySelectorAll('[data-backtop]').forEach(function (btn) {
  var sync = function () { btn.classList.toggle('is-visible', window.scrollY > 400); };
  window.addEventListener('scroll', sync, { passive: true });
  sync();
  btn.addEventListener('click', function () {
    window.scrollTo({ top: 0, behavior: 'smooth' });
  });
});