I haven't spent a lot of time with the style customization tbh. I don't know about horizontal lines, but my theme has each post in its own box (i mean you can look at my page and see it in action). I don't think the individual colors thing was imported as a feature, but I don't know. I wanted one where I could put sidebar things on the right and choose which sidebar elements were there, and in a color scheme that was pleasing to my eyes.

Have you tried clicking on the themes to preview them?

https://dw-news.dreamwidth.org/38065.html has a 101 for new users from LJ land.