If you were hoping this would be easy, the bad news is that there simply isn't a quick and simple way to do this -- the text cursor is not something you can just change with a couple of lines of javascript or CSS.
If you really want to do this, you're going to need to write your own entire text input system in javascript -- display the cursor yourself, wait for key presses, print them to the screen, handle anything like word-wrapping manually.... it's a fair bit of work.
Fortunately, others have already done this work and made it available to share, so I suggest your best starting point would be to take a look at some existing examples and see how they've done it.
Here's one I found with a quick bit of googling: http://terminal.jcubic.pl/. There are plenty of others you could try as well though.
Hope that helps.
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