使背景图像在单击其中一个文本输入以弹出键盘时不会“挤压”

body {
  background-image: url('background.jpg');
  background-position: center center;
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
}

var input = document.getElementById('text-input');
input.addEventListener('focus', function() {
  document.body.style.backgroundPosition = '0 0';
});
input.addEventListener('blur', function() {
  document.body.style.backgroundPosition = 'center center';
});