背景图像无法在iPhone上正确显示（居中）

here is my css class

这是我的CSS课程

   .parallax {
         background: url(../images/indexParallax.png) no-repeat center center fixed; 
         display: table;
         height: 100%;
         position: relative;
         width: 100%;
         -webkit-background-size: cover;
         -moz-background-size: cover;
         -o-background-size: cover;
         background-size: cover;
         overflow: hidden;
}
   .parallax