“内容：”上的CSS动画在Safari和Firefox上不起作用

@asimovwasright的答案是正确的。

为了避免在CSS上发生太多重复，我将

@for

.hey {    span {        color: transparent;        animation: heyThere 500ms ease-out;        animation-fill-mode: forwards;        $chars: 8;        @for $i from 1 through $chars { &:nth-of-type(#{$i}) {     animation-delay: 1200+70ms*$i; }        }    }}

和HTML：

<h2 >   <span>H</span>   <span>e</span>   <span>y</span>   <br>   <span>t</span>   <span>h</span>   <span>e</span>   <span>r</span>   <span>e</span></h2>