.particles {
    background: #fafafa;
    border: 5px solid #fafafa;
    border-radius: 3px;
    height: 400px;
    margin: 10px auto;
    position: relative;
    width: 90%;
}

.particle {
    $side: 20px;

    background: url('../res/seahorse.svg');
    background-size: $side $side;
    height: $side;
    position: absolute;
    width: $side;
}