背景渐变，兼容所有手机端

#div{
    width:400px;
    height:400px;
    background:-moz-linear-gradient(top, #198bc9, rgba(255, 255, 255, 0.5));  
     background:-webkit-gradient(linear, 0 0, 0 bottom, from(#198bc9), to(rgba(255,255,255, 0.5)));  
     background:-o-linear-gradient(top, #198bc9, rgba(255, 255, 255, 0.5)); 
}