A huge part of the appeal of C64-style BASIC is the lack of distractions. I mean, you're already talking about CSS! :-)
A better match than Javascript (which doesn't have an interactive console, and HTML+JS is event-driven) would be Python.
A better match than Javascript (which doesn't have an interactive console, and HTML+JS is event-driven) would be Python.
node.js has a text console if you don't want the web browser attached.
A super limited one. You can't edit code there.