SOURCE

<span class="box">
    哈哈哈哈哈哈红红火火恍恍惚惚
</span>

.box {
    border: 1px solid red;
    display: inline-block;
    padding: 10px;
    /* width: 20px; */
    /* 设置透明 */
    color: transparent;
    background: -webkit-linear-gradient(30deg,red 15%,blue 50%,green 75%,yellow 100%);
background-clip: text;
-webkit-background-clip: text;
-webkit-text-fill-color: transparent;
background-size: auto;
animation: gradienText 100s  infinite linear;
}
@keyframes gradienText {
    from{
        background-position: 0
    }
    to{
        background-position: 28000px
    }
}