将html的类改为gray，引用下面的样式即可

.gray{
  -webkit-filter: grayscale(100%); 
  -moz-filter: grayscale(100%); 
  -ms-filter: grayscale(100%); 
  -o-filter: grayscale(100%);
  filter: grayscale(100%);
  filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
  filter: progid: DXImageTransform.Microsoft.BasicImage(grayscale = 1); 
  -webkit-filter: grayscale(1)
}