Hi.
To change the post details background color to black, please use the custom CSS below:
.single-post .site-content-single-post .blog-wrap .blog-inner article .entry-post-meta-wrap .entry-meta-info h1 {
color: #fff;
}
.single-post .site-content-single-post .blog-wrap .blog-inner article {
background-color: #000;
color: #fff;
box-shadow: none;
}
.single-post #yolo-content-wrapper {
background: #000;
}
2. For the duplicate post title. The white "underground news" is the menu item, and the second title "underground news" is the breadcrumb of the post. When you click on breadcrumb, it will link to the category archive page.
3. To change the post details URL, please check the permalink config.
Please recheck it.
Thanks.