*{
    font-family: 'Microsoft Yahei',Helvetica,sans-serif;
}

html{
   margin: 0px;
   padding: 0px;
}

body{
    background-color: silver;
    margin: 0px;
    padding: 0px;
    margin-left: 30px;

}
#backWhole{
    width: 100%;
    height: 100%;
    max-width: 100%;
    max-height: 100%;
    position: fixed;
    background-color: #000000;
}


.back_show{
   animation: back_show_animat 0.6s ease-in-out;
   animation-fill-mode:  forwards ;
}
.back_hide{
   animation: back_hide_animat 0.6s ease-in-out;
   animation-fill-mode:  forwards ;
}


@keyframes  back_show_animat{
   0%{
       opacity: 0;
   }
   100%{
       opacity: 0.6;
   }
}
@keyframes  back_hide_animat{
   0%{
       opacity: 0.6;
   }
   100%{
       opacity: 0;
   }
}