Set custom theme if post has defined tag

Developer help
1

Hello.
How can I automatically set a defined template for the post if it has a defined tag?
I suppose this rule I have to set in code of post theme file, right?

2

Options:

  1. Edit routes.yaml and write a custom template
  2. Edit post.hbs to include some styling logic
  3. Add styling for .tag-yourtagname to your css or code injection. Ghost themes typically add a class for each tag on the post.

I’d start with option 3 unless you need major rearrangement instead of a little restyling.