如何将CSS按钮的Hover发光动画改为持续生效？

现有代码通过:hover触发按钮的发光动画，要实现无需hover操作就让发光效果持续生效，只需调整伪元素的opacity属性即可，具体修改步骤如下：

1. 找到.drts-bs-btn-outline-primary:before规则，将其中的opacity: 0改为opacity: 1
2. 可删除.drts-bs-btn-outline-primary:hover:before规则（不再需要hover触发），保留也不会影响最终效果

修改后的完整代码：

.drts-bs-btn-outline-primary {
    width: 220px;
    height: 50px;
    border: none;
    outline: none;
    color: #fff;
    background: #111;
    cursor: pointer;
    position: relative;
    z-index: 0;
    border-radius: 10px;
}

.drts-bs-btn-outline-primary:before {
    content: '';
    background: linear-gradient(45deg, #ff0000, #ff7300, #fffb00, #48ff00, #00ffd5, #002bff, #7a00ff, #ff00c8, #ff0000);
    position: absolute;
    top: -2px;
    left:-2px;
    background-size: 400%;
    z-index: -1;
    filter: blur(5px);
    width: calc(100% + 4px);
    height: calc(100% + 4px);
    animation: glowing 20s linear infinite;
    opacity: 1; /* 此处修改为1 */
    transition: opacity .3s ease-in-out;
    border-radius: 10px;
}

.drts-bs-btn-outline-primary:active {
    color: #000
}

.drts-bs-btn-outline-primary:active:after {
    background: transparent;
}

/* 可删除该hover规则，也可保留 */
/* .drts-bs-btn-outline-primary:hover:before {
    opacity: 1;
} */

.drts-bs-btn-outline-primary:after {
    z-index: -1;
    content: '';
    position: absolute;
    width: 100%;
    height: 100%;
    background: #111;
    left: 0;
    top: 0;
    border-radius: 10px;
}

@keyframes glowing {
    0% { background-position: 0 0; }
    50% { background-position: 400% 0; }
    100% { background-position: 0 0; }
}

原理说明 #

原本的发光动画glowing其实一直处于运行状态，只是:before伪元素默认opacity: 0所以不可见。hover触发时只是将opacity改为1显示效果，直接把opacity设为1就能让发光效果始终展示，无需hover操作触发。

内容的提问来源于stack exchange，提问作者CcCcSS