Hedgedoc CSS to specify a common background image in CSS instead of manually and set an opacity to the background except for the title page

hedgedoc-background.css

/* set the background image for all pages which have an (empty) <!-- .slide: data-background="" --> marker */
/* create overlay with background image */
.slide-background-content::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-image: url("image-url");
    background-size: cover;
    background-position: center;
}
/* set the opacity of all backgrounds except on the title page to 30% */
.backgrounds > .slide-background:not(:first-child) .slide-background-content::before {
    opacity: 0.3;
}
/* place the a logo on all backgrounds except on the title page */
.backgrounds > .slide-background:not(:first-child) .slide-background-content {
    position: relative;
    background-image: url('logo-url'); 
    background-position: right 30px bottom 30px;
    background-repeat: no-repeat;
    background-size: 50%;
}