css实现文字淡入淡出

.first-words{ //针对每秒写样式    opacity: 0;      /*实先规定文字的状态是不显示的*/    animation: fade-in 4s ease 0s 1;    /*调用名称为fade-in的动画，全程动画显示时间4S，进入方式为ease，延时0S进入，播放次数1次*/    -webkit-animation: fade-in 4s ease 0s 1;    -moz-animation: fade-in 4s ease 0s 1;    -o-animation: fade-in 4s ease 0s 1;    -ms-animation: fade-in 4s ease 0s 1;        /*规定动画的最后状态为结束状态*/    animation-fill-mode:forwards;    -webkit-animation-fill-mode: forwards;        -o-animation-fill-mode: forwards;       -ms-animation-fill-mode: forwards;         -moz-animation-fill-mode: forwards; }.second-words{     opacity: 0;        animation: fade-in 4s ease 2s 1;    -webkit-animation: fade-in 4s ease 2s 1;    -moz-animation: fade-in 4s ease 2s 1;    -o-animation: fade-in 4s ease 2s 1;    -ms-animation: fade-in 4s ease 2s 1;        /*规定动画的最后状态为结束状态*/    animation-fill-mode:forwards;    -webkit-animation-fill-mode: forwards;        -o-animation-fill-mode: forwards;       -ms-animation-fill-mode: forwards;         -moz-animation-fill-mode: forwards; }.third-words{     opacity: 0;        animation: fade-in 4s ease 4s 1;    -webkit-animation: fade-in 4s ease 4s 1;    -moz-animation: fade-in 4s ease 4s 1;    -o-animation: fade-in 4s ease 4s 1;    -ms-animation: fade-in 4s ease 4s 1;        /*规定动画的最后状态为结束状态*/    animation-fill-mode:forwards;    -webkit-animation-fill-mode: forwards;        -o-animation-fill-mode: forwards;       -ms-animation-fill-mode: forwards;         -moz-animation-fill-mode: forwards; }