#about {
    position: relative;
    margin-top: 120px;
}

#about::after {
    content: "";
    background: url('/images/logo.png') no-repeat center;
    background-size: contain;
    position: absolute;
    top: 5%;
    right: 10%;
    width: 400px;
    height: 400px;
    opacity: 0.2;
    z-index: -1;
}

@media (max-width: 768px) {

    #about::after {
        width: 300px;  
        height: 300px;
    }
}