<div class="btn-dl-surface">
  <button class="btn-dl">
    <span class="btn-dl-fill" aria-hidden="true"></span>
    <span class="btn-dl-label">
      <span class="btn-dl-arrow" aria-hidden="true">↓</span>
      <span>Download File</span>
    </span>
    <span class="btn-dl-done">✓&nbsp;Complete</span>
  </button>
</div>

.btn-dl-surface {
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 32px 40px;
  background: #f2efe9;
  border-radius: 16px;
}
.btn-dl {
  position: relative;
  width: 200px;
  height: 52px;
  border: 2px solid #1a1814;
  border-radius: 26px;
  background: transparent;
  cursor: pointer;
  overflow: hidden;
  user-select: none;
}
.btn-dl-fill {
  position: absolute;
  inset: 0;
  background: #1a1814;
  border-radius: 24px;
  transform: translateX(-100%);
}
.btn-dl-label {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  z-index: 1;
  font-family: ui-sans-serif, system-ui, sans-serif;
  font-size: 13px;
  font-weight: 600;
  color: #1a1814;
  transition: color 0.2s;
}
.btn-dl-arrow { font-size: 16px; }
.btn-dl-done {
  position: absolute;
  inset: 0;
  z-index: 2;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  font-family: ui-sans-serif, system-ui, sans-serif;
  font-size: 13px;
  font-weight: 600;
  color: #fff;
  opacity: 0;
  transform: scale(0.8);
  transition: opacity 0.3s, transform 0.3s;
}
.btn-dl.is-loading .btn-dl-fill {
  transform: translateX(0);
  transition: transform 1.4s cubic-bezier(.4,0,.2,1);
}
.btn-dl.is-loading .btn-dl-label { color: #fff; }
.btn-dl.is-loading .btn-dl-arrow { animation: btn-dl-bounce 0.6s infinite alternate; }
@keyframes btn-dl-bounce {
  from { transform: translateY(-3px); }
  to   { transform: translateY(3px); }
}
.btn-dl.is-done .btn-dl-fill { transform: translateX(0); }
.btn-dl.is-done .btn-dl-label { opacity: 0; }
.btn-dl.is-done .btn-dl-done { opacity: 1; transform: scale(1); }
@media (prefers-reduced-motion: reduce) {
  .btn-dl.is-loading .btn-dl-arrow { animation: none; }
}

document.querySelectorAll('.btn-dl').forEach(function (btn) {
  var busy = false;
  btn.addEventListener('click', function () {
    if (busy) return;
    busy = true;
    btn.classList.add('is-loading');
    setTimeout(function () {
      btn.classList.remove('is-loading');
      btn.classList.add('is-done');
      setTimeout(function () {
        btn.classList.remove('is-done');
        busy = false;
      }, 2500);
    }, 1600);
  });
});