/** 白屏阶段会执行的 CSS 加载动画 */
#app-loading {
    position: relative;
    top: 45vh;
    margin: 0 auto;
    color: #409eff;
    font-size: 12px;
}
#app-loading,
#app-loading::before,
#app-loading::after {
    width: 2em;
    height: 2em;
    border-radius: 50%;
    animation: 2s ease-in-out infinite app-loading-animation;
    }
#app-loading::before,
#app-loading::after {
    content: "";
    position: absolute;
    }
#app-loading::before {
    left: -4em;
    animation-delay: -0.2s;
}
@keyframes app-loading-animation {
    0%,
    80%,
    100% {
      box-shadow: 0 2em 0 -2em;
    }
    40% {
      box-shadow: 0 2em 0 0;
    }
}