.first-section-image img {
    width: 100%;
    margin-top: -4px;
}

@media (max-width:800px) {
    .first-section-image img {
        display: none;
    }
    .first-section-image {
        background: url("../images/first-section-responsive.jpg") no-repeat center;
        min-height: 600px;
        background-size: cover;
    }
}