CSS Border Effect Animation

How to Create an Animated Radial Border Effect on Buttons with CSS

Watch the full tutorial here:

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link rel="stylesheet" href="./style.css">
    <title>Button border gradient effect</title>
</head>

<body>
    <button id="button">Suscribe</button>
</body>

</html>

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

body {
    width: 100%;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #111;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

@property --angle {
    syntax: "<angle>";
    initial-value: 0deg;
    inherits: false;
}

#button {
    padding: 15px 50px;
    font-size: 25px;
    border: none;
    border-radius: 100px;
    background-color: #112C55;
    color: #FFF;
    font-weight: 500;
    text-transform: uppercase;
    position: relative;

    &::after,
    &::before {
        content: '';
        position: absolute;
        width: 100%;
        height: 100%;
        border-radius: 100px;
        background-image: conic-gradient(from var(--angle), red, blue, yellow, red);
        top: 50%;
        left: 50%;
        translate: -50% -50%;
        z-index: -10;
        padding: 3px;
        animation: 3s spin linear infinite;
    }

    &::before {
        filter: blur(1.5rem);
        opacity: 0.5;
    }
}

@keyframes spin {
    from {
        --angle: 0deg;
    }

    to {
        --angle: 360deg;
    }
}