I currently have my blog page set to a custom child theme, but when I go to an individual blog post, it uses the default template from my index.php. What I want is to have the individual post page have its own styling, basically a child theme specifically for the individual posts, but not for the Blog index. Does anyone know how I can do this?
In other words my default page has a container that is too wide, so I want another template with a container size that is more suitable for reading the full article.
Make a page called single.php in your child theme and add custom classes and containers there. Index.php is the fall back for everything. If your child theme doesn't have a single.php, it'll use index.php instead. You can also have single-{post-type}.php or single-{post-type}-{slug}.php if you need more granular control.
https://developer.wordpress.org/themes/basics/template-hierarchy/#single-post