I see what you mean. As far as I’m aware, I think that’s builtin to the web server software. So it’s not something you can change in Nginx to make it look like Caddy, nor can you modify Caddy’s configuration. I think the most Caddy does is change the background colors and font colors to match the user’s browser’s preference of light or dark mode, but this is builtin to the source code, so you can’t modify the colors unless you fork Caddy and change the source code yourself.