body {
    margin: 0;
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: black;
}

.container {
    width: 30em;
    height: 30em;
    font-size: 10px;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    transform: rotate(-135deg);
}

.container span {
    position: relative;
}

.container span::before,
.container span::after 
{
    content: '';
    position: absolute;
    box-sizing: border-box;
    border-style: none solid solid none;
    animation: 
        animate-border-width 1.6s linear infinite,
        animate-border-color 1.6s linear infinite,
        animate-scale 1.6s linear infinite;
}

.container span::after {
    animation-delay: -0.8s;
}

@keyframes animate-border-width {
    0%, 100%{
        border-width: 0.1em;
    }

    25% {
        border-width: 1.5em;
    }
}

@keyframes animate-border-color {
    0%, 25% {
        border-color: tomato;
    }

    50%, 75% {
        border-color: gold;
    }

    100% {
        border-color: black;
    }
}

@keyframes animate-scale {
    from {
        width: 1%;
        height: 1%;
    }

    to {
        width: 100%;
        height: 100%;
    }
}