.cb-slideshow,
.cb-slideshow:after {
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0px;
    left: 0px;
    z-index: 0; 
}
.cb-slideshow { 
    margin: 0; 
    padding: 0; 
    list-style: none;
    background-image: url(../images/opt3.jpg); /* Set your static image here */
    opacity: 1;
    background-size: cover;
    background-position: 50% 50%;
    background-repeat: no-repeat;
    -webkit-filter: brightness(120%); /* Increase brightness */
    filter: brightness(120%); /* Increase brightness */
}

/* Remove or comment out all other .cb-slideshow li span and keyframes definitions as they are no longer needed */
/*
.cb-slideshow li span { 
    ...
}
@-webkit-keyframes imageAnimation { 
    ...
}
...
*/