How do you change a web sites .css client-side? What do I do with the above code? I've been out of the hard-core web design stuff for too long, but I really would like the black background back.

John said this also back in January 2018 when he said Google Image search does not index and rank images from CSS background code.

Use CSS code to style your site headers with borders and other design elements. HTML and CSS use a box model, which means that page elements include margins, padding, background colors and ...

How to Customize CSS in Blogspot. The Blogger Template Designer allows you to insert custom CSS code to change your blog's appearance. You can access the advanced settings of the Template Designer ...

Google says images styled with CSS won’t be indexed in Image Search, advising developers to use HTML tags for important visuals.