For a lightweight personal blogging platform that meets your requirements, consider using a static site generator like Hugo (gohugo.io) or Jekyll (jekyllrb.com), which support markdown, syntax highlighting, and customizable themes. You can host your site for free on GitHub Pages (pages.github.com) and automate deployment with GitHub Actions. Hexo (hexo.io) and Blades (getblades.org) are also good alternatives.