如何在提交后使用背景模糊的iframe顯示頁面

function unHide() {
  document.getElementById('background').style.display = 'flex';
}

.background {
  display: flex;
  justify-content: center;
  align-items: center;
  position: absolute;
  top: 0%;
  left: 0%;
  width: 100%;
  height: 100%;
  background-color:rgba(0,0,0,0.3);
  z-index: 9999;
  display: none;
}

<button onclick="unHide()">Cick Me</button>
<div class="background" id="background">
  <iframe width="350" height="315" src="https://www.youtube.com/embed/owsfdh4gxyc" frameborder="0" allowfullscreen></iframe>
</div>