背景颜色透明

.loading{filter:progid:DXImageTransform.Microsoft.gradient(enabled='true',startColorstr='#CC000000', endColorstr='#CC000000');background:rgba(0,0,0,0.8);}
:root .loading{filter:progid:DXImageTransform.Microsoft.gradient(enabled='true',startColorstr='#00000000', endColorstr='#00000000');}/*for IE9*/
:root .loading{filter:none;}/*for IE9*/