style.css

*
{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background: #111;
}
h2
{
    display:flex;
    color: transparent;
    font-size: 50px;
}
h2 span
{
    animation: animate 3s linear infinite;
    animation-delay: calc(0.1s * var(--i));
}
@keyframes animate
{
    0%
    {
        color: #fff;
        filter: blur() hue-rotate(0deg);
        text-shadow: 0 0 10px #00b3ff,
        0 0 20px #00b3ff,
        0 0 40px #00b3ff,
        0 0 120px #00b3ff,
        0 0 200px #00b3ff,
        0 0 300px #00b3ff,
        0 0 400px #00b3ff;
    }
    30%,70%
    {
        color: #fff;
        filter: blur() hue-rotate(360deg);
        text-shadow: 0 0 10px #00b3ff,
        0 0 20px #00b3ff,
        0 0 40px #00b3ff,
        0 0 120px #00b3ff,
        0 0 200px #00b3ff;
    }
    100%
    {
        color: transparent;
        box-shadow: none;
        filter: blur() hue-rotate(0deg);
    }
}