.dynamic_1, .dynamic_2, .dynamic_3{
    flex:1;
margin-top: 20rpx;
/*background-size: 100% 100%;*/
background-size: cover;
position: relative;
text-align: center;
}
.dynamic_1{
    background-image: url('http://app.maidiyun.com/images/dtjq/dtjw_bg1.png');
}
.dynamic_2{
    background-image: url('http://app.maidiyun.com/images/dtjq/dtjw_bg3.png'
 
);
}
.dynamic_3{
    background-image: url('http://app.maidiyun.com/images/dtjq/dtjw_bg2.png');
}

將background改為background-image