It works just fine for me. I opened the "GettingStarted.textastic" file (which is a Markdown file), entered "<" and a list of html tags popped up.
There is no code completion support yet for C#. I fixed a bug in the latest version that showed C functions and code completions in C# files which was wrong.
You can find the latest code completion files at https://github.com/blach/Textastic-Customization/tree/master/CodeCompletion
For CSS, code completion of properties like "border" or "background-color" should work.
I saw that and now I know for certain. Have a nice day.
Customer support service by UserEcho