.img-main {
    background-color: #394859;
    background-image: url('images/img-main.jpg');
    background-image: linear-gradient( 90deg, #2a333200 30%, #5a0aad54 70%), url(images/img-main.jpg);
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
}

@media (max-width: 770px) {
    .img-main {
        background-image: linear-gradient( 90deg, #2a333200 0%, #5a0aad54 50%), url(images/img-main.jpg);
    }
}