body {
    background: url('/img/IMG_3583.jpg');
    background-size: cover;
    background-position: center;
}

body::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    z-index: -1;
}

.container {
    position: relative;
    z-index: 1;
}

.btn {
    padding: 10px 20px;
}