Make textbox focus clearer

[kornelski]

To me difference between focused and unfocused text box is too subtle, and I often find myself accidentally activating browser shortcuts when I've meant to type code.

Fortunately playpen remembers text when I exit the page via accidental backspace (thanks for that), but I'd rather not make that mistake in the first place.

I think the most deceptive thing for me is that current line is highlighted in yellow even if the box is not in focus.

When text entry doesn't have focus I suggest removing current-line highlight or changing it to light gray. Darker/lighter border of the text box would be useful as well.

[nightwing]

ajaxorg/ace#2397 changes line highlight to be gray in blurred state