footer {
    background-color: #3f3f3f; 
    padding: 15px 6%; 
    text-align: center;
    box-shadow: 0 -5px 10px #3f3f3f;
    opacity: 0.95;
    left: 0;
    width: 100%;
    bottom: 0;
    margin-top: auto;
    z-index: 4;
}