I'm using pandoc for generating pdf/epub ebooks from GitHub style markdown. The default output is good enough and there are various themes that can be selected. But I wanted to customize a lot of things like chapter breaks, background color for inline code, bullet styles, blockquote style, etc. I didn't know Latex but was able to find snippets from stackexchange sites to suit my needs. I wrote a blog post on this: https://learnbyexample.github.io/customizing-pandoc/