style.css

.stApp {
     background-image: url('https://i.postimg.cc/9fvk4CNd/modern.png'); 
    background-size: cover;
    background-position: center;
    background-repeat: no-repeat;
    /*background: linear-gradient(to right, #006747, #9B111E); 
    background-size: cover;
    height: 100vh;
    margin: 0;
    font-family: Arial, sans-serif;
    position: relative;  To position the overlay */
}

.stApp::after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.8); /* Black overlay with 50% opacity */
    z-index: -1; /* Place the overlay behind the content */
}