SOURCE

<p>asdasdasd</p>
<div class="ys-popup">
    <div class="ys-popup-content ys-popup-center">
      <div class="">11111</div>
    </div>
  </div>

.ys-popup {
  position: fixed;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  background-color: rgba(0, 0, 0, 0.5);
  transition: opacity 350ms ease 0s;
}

.ys-popup-content {
  position: absolute;
  max-height: 100%;
  overflow-y: auto;
  background-color: #fff;
  padding: 10px 20px;
  border-radius: 5px;
  transition: transform 0.2s;
}
.ys-popup-center {
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}