I take notes in Markdown in an editor that formats it automagically called IA Writer. Bullets are indented, headlines bolded and out-dented, etc.
I'm sure there are a few more markdown "WYSIWYM" I'm forgetting...
To build your own see also https://simplemde.com/. Basically CodeMirror is friendly to mixed-font syntax highlighting.
Also yours truly https://mathdown.net