.fade-enter{
    opacity:0;  /* opacity:0.01 */
}
.fade-enter-active{
    opacity:1;
    transition: opacity 500ms ease-in;
}
.fade-exit{
    opacity:1;
}
.fade-exit-active{
    opacity:0;  /* opacity:0.01 */
    transition: opacity 500ms ease-in;
}