• HTML
• CSS

HTML

<div class="loader">
    <div style="--i:1;"></div>
    <div style="--i:2;"></div>
    <div style="--i:1;"></div>
</div>

CSS

*{
    margin:0;
    padding:0;
    box-sizing:border-box;
}
body{
    display:flex;
    justify-content:center;
    align-items:center;
    min-height:100vh;
    background:#1488cc;
    background-image:linear-gradient(to bottom, #1488cc, #85eae9);
}
.loader div{
    width:40px;
    height:40px;
    background:rgba(0,0,0,0.4);
    display:inline-block;
    border-radius:50%;
    transform:scale(0);
    animation:animar 1s linear infinite;
    animation-delay:calc(0.4s * var(--i));
}

@keyframes animar{
    0%{
        transform:scale(0);
    }
    50%{
        transform:scale(0.8);
    }
    100%{
        transform:scale(0);
    }
}