<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;
 }
}