<div class="box">
    you are my<br>
    FAVORITE
</div>

html,
body,
.box {
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
}

body {
    background: #222;
}

.box {
    color: white;
    font-size: 2.5em;
    width: 10em;
    height: 5em;
    background: #111;
    font-family: sans-serif;
    line-height: 1.5em;
    text-align: center;
    border-radius: 0.2em;
}

.box {
    position: relative;
}

.box::after {
    content: '';
    position: absolute;
    width: 102%;
    height: 104%;
    background-color: orange;
    z-index: -1;
    border-radius: 0.2em;
}

.box::after {
    /*background-color: orange;*/
    background-image: linear-gradient(60deg, aquamarine, cornflowerblue, goldenrod, hotpink, salmon, lightgreen, sandybrown, violet);
}

.box::after {
    background-size: 300%, 300%;
    animation: animate_bg 5s ease infinite alternate;
}

@keyframes animate_bg {
    0% {
        background-position: 0%, 50%;
    }

    50% {
        background-position: 100%, 50%;
    }

    100% {
        background-position: 0%, 50%;
    }
}

.box {
    animation: animate_text 2s linear infinite alternate;
}

@keyframes animate_text {
    from {
        color: lime;
    }

    to {
        color: yellow;
    }
}