<div class="main">
    <div class="circle">circle</div>
</div>

// Global Styles

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

html,
body {
    width: 100%;
    height: 100%;
    overflow: hidden; 
}

// Main Styles

.main {
    width: 100%;
    height: 100%;
    background: #161616;
    display: flex;
    justify-content: center;
    align-items: center;
}
.circle {
    font-family: monospace;
    font-size: 10rem;
    color: #fff;    
    transform: translateX(-50%) translateY(-50%) rotate(0deg);
    text-shadow: 0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22);
    top: 50%;
    left: 50%;
    position: absolute;
    &::after,
    &::before {
        content: "";
        border: 1rem solid slateblue;
        z-index: 1;
        padding: .9em .4em;
        width: 20%;
        top: 50%;
        left: 50%;
        position: absolute;
        border-radius: 10rem;
        animation: circle-animation 4s linear infinite forwards;
    }
}

.circle::after {
    border-color: rgba(0, 0, 0, 0) rgba(0, 0, 0, 0) slateblue slateblue;
    box-shadow: 0 19px 38px rgba(0,0,0,0.30), 0 15px 12px rgba(0,0,0,0.22);
}

.circle::before {
    border-color: tomato tomato rgba(0, 0, 0, 0) rgba(0, 0, 0, 0);
    z-index: -1;
}

@keyframes circle-animation {
    0% {
        transform: translateX(-50%) translateY(-50%) rotate(0deg);
        width: 75%
    }

    50% {
        transform: translateX(-50%) translateY(-50%) rotate(180deg); 
        width: 100%;   
    }

    100% {
        transform: translateX(-50%) translateY(-50%) rotate(360deg);
        width: 75%;
    }
}