/* body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
} */

/* *,
*::before,
*::after {
    box-sizing: border-box;
} */

@keyframes rotate {
    100% {
        transform: rotate(1turn);
    }
}

.rainbow-box {
    position: relative;
    z-index: 0;
    /* width: 400px;
    height: 300px; */
    border-radius: 10px;
    overflow: hidden;
    padding: 1rem;
}

.rainbow-box::before {
    content: '';
    position: absolute;
    z-index: -2;
    left: -50%;
    top: -50%;
    width: 200%;
    height: 200%;
    background-color: #399953;
    background-repeat: no-repeat;
    background-size: 50% 50%, 50% 50%;
    background-position: 0 0, 100% 0, 100% 100%, 0 100%;
    background-image: linear-gradient(#399953, #399953), linear-gradient(#fbb300, #fbb300), linear-gradient(#d53e33, #d53e33), linear-gradient(#377af5, #377af5);
    animation: rotate 4s linear infinite;
}

.rainbow-box::after {
    content: '';
    position: absolute;
    z-index: -1;
    left: 6px;
    top: 6px;
    width: calc(100% - 12px);
    height: calc(100% - 12px);
    background: white;
    border-radius: 5px;
    animation: opacityChange 3s infinite alternate;
}

@keyframes opacityChange {
    50% {
        opacity: 1;
    }

    100% {
        opacity: 0.5;
    }
}